Wallpaper Calculator (How Many Rolls, with Pattern Repeat and Waste)

Enter the room size (length × width or perimeter), the ceiling height, the doors and windows, and the wallpaper width, pattern repeat and waste percentage. Roll length and price are optional (if left blank, they are not calculated).

Units

How to enter the room size

Room length (m)

Room width (m)

Ceiling height (m)

Extra area (m², optional)

Openings (doors, windows and other parts you do not paper; blank rows are ignored)

	Width (m)	Height (m)	Count
1
2
3
4
5
6

Wallpaper width (cm)

Pattern repeat (cm, 0 if plain)

Trim allowance (cm, top + bottom)

Waste (%)

Roll length (m, optional)

Wallpaper price ($, optional)

Room sizes, ceiling height and openings are in meters (m); wallpaper width, pattern repeat and trim allowance are in centimeters (cm). For plain wallpaper, set the pattern repeat to 0.

Result and figure

Enter the room size, the ceiling height, the wallpaper width and so on in the fields on the left and press "Calculate". The result will appear here.

[ CLOSE ]

What you can do on this page
What is this calculation used for?
How to Use
Formulas and figures
Symbols and terms
- Symbols
- Terms
Good to know before you start
How to calculate it in Excel
How to calculate it in Google Sheets
How to calculate it in Python
How to write it in LaTeX and other math languages (copy and paste)
How to have ChatGPT do the calculation
DataChef Features
Related Features
NumberChef Calculators List

What you can do on this page

Enter either the room length × width or the perimeter, plus the ceiling height, and you get the length of wallpaper you need on the spot
The number of strips comes from the net wall area, with doors and windows (up to 6 sizes × count) taken out, so you do not buy far too much
For patterned wallpaper, the length of each strip is rounded up to a whole number of pattern repeats (you can see in the formulas how much pattern matching adds)
Enter the waste percentage (10% by default), the roll length and the price to also get the length with waste, the number of rolls (double rolls are standard in the US) and an estimated cost
A plain-language explanation of the formulas and copy-and-paste formulas for Excel, Google Sheets and Python are all on this page

The amount is an estimate based on area. What you really need depends on the shape of the walls, how the pattern is matched and your experience, so it is common to buy extra using the waste percentage. To paper the ceiling too, enter the ceiling area in "Extra area". By default this page works in feet and inches; switch "Units" above the calculator to Metric to use m and cm.

What is this calculation used for?

Shopping for a DIY wallpaper project

Peel-and-stick wallpaper has made DIY wallpapering popular, even for renters. For a 12 × 10 ft room with an 8 ft ceiling, one door and one window, plain 20.5 in paper takes 24 strips × 100 in = 200 ft, or about 220 ft with 10% waste.
Switch to a paper with a 21 in repeat and each strip becomes 105 in, so the same room needs 231 ft. In both cases one 33 ft double roll gives only 3 strips, so you need 8 double rolls. Knowing this before you buy saves you from running short on the last wall.

An accent wall in a different color or pattern

Papering just one wall, such as the wall behind the TV or the bed, is one of the most popular DIY projects. For a wall 10 ft wide with an 8 ft ceiling, choose "Perimeter" and enter 10: $\lceil 120 \div 20.5 \rceil = 6$ strips. Plain paper takes 6 × 100 in = 50 ft, or 55 ft with 10% waste (2 double rolls).
With a 24 in repeat, each strip is $24 \times \lceil 100 \div 24 \rceil = 120$ in (10 ft), so you need 60 ft, or 66 ft with waste. The larger the repeat, the more the length changes.

Checking the quantities in a remodeling quote

A quote for wallpapering often lists the quantity by area, such as "wallpaper install, 319 sq ft × unit price", and that square footage is calculated the same way as the net wall area on this page (perimeter × ceiling height − openings).
If you work out the area yourself with the same formula, it is easier to check in the meeting whether the quantity matches the room and whether the ceiling is included. (A real quote also includes surface preparation, removal of old paper and trip charges, so the square footage alone cannot tell you whether the price is fair.)

Planning the interior of a shop or office with a contractor

For a small cafe or office, the owner often chooses wallpaper samples and the contractor works out the quantities. Wallpaper catalogs always list the width and the pattern repeat, and a paper with a large repeat needs more length for the same wall, which raises the material cost.
Being able to estimate "how much more this pattern needs" lets you balance design and budget yourself. Patterned paper also takes the installer more time, so the labor cost may change too.

Building walls for a stage set or a photo set

For a stage backdrop or a photo booth at an event, you make "room walls" by covering plywood or fabric panels with wallpaper. Enter the total width of the panels as the perimeter to get the length you need.
Patterned papers such as brick or wood grain need pattern matching, and if you do not allow for the rounding up by the repeat, the last strip often comes up short. On a tight budget, such as a school play, this calculation really helps.

Formulas and figures

Net wall area (the area minus openings)

Figure

Standard notation (the usual math form)

$A$ $=$ $L$ $\times$ $H$ $-$ $D$

In words (symbols replaced with words)

④ $A$: net wall area $=$ ① $L$: room perimeter $\times$ ② $H$: ceiling height $-$ ③ $D$: total area of openings

The formula in words

① Take the $L$: room perimeter

② multiply it by the $H$: ceiling height to get the area of the walls laid out in a row

③ subtract the $D$: total area of openings (width × height × count of each door and window, added up)

④ and you get the $A$: net wall area

Quick example

A 12 × 10 ft room has a perimeter of $2 \times (12 + 10) = 44$ ft. With an 8 ft ceiling, one door (3 × 7 ft) and one window (3 × 4 ft), the net wall area is

net area $A$ $=$ perimeter (44 ft) $\times$ ceiling height (8 ft) $-$ openings (33 ft²)

$3 \times 7 + 3 \times 4 = 21 + 12 = 33\,\mathrm{ft^2}$

$44 \times 8 - 33 = 352 - 33 = 319\,\mathrm{ft^2}$

Key idea

There are four walls to paper, but they all have the same ceiling height, so you can join them into one row, a rectangle of perimeter × ceiling height, and get the area in one step. If you enter length × width, the perimeter is $L = 2 \times (\text{length} + \text{width})$. For just one wall (an accent wall), enter only that wall's width as the perimeter and the same formula works. Doors and windows get no wallpaper, so subtract them. Some people leave small windows and outlets in as extra margin instead. To paper the ceiling too, enter the ceiling area in "Extra area" and it is added to $A$.

Length per strip (with pattern match and trim allowance)

Figure

Standard notation (the usual math form)

$\ell$ $=$ $R$ $\times$ $\lceil$ $($ $H$ $+$ $m$ $)$ $\div$ $R$ $\rceil$

In words (symbols replaced with words)

⑤ $\ell$: length per strip $=$ ④ $R$: pattern repeat $\times$ $\lceil$ $($ ① $H$: ceiling height $+$ ② $m$: trim allowance $)$ $\div$ ③ $R$: pattern repeat $\rceil$

The formula in words

① Take the $H$: ceiling height

② add the $m$: trim allowance to get the least length one strip needs

③ divide by the $R$: pattern repeat and round up (= how many repeats are enough)

④ multiply back by the $R$: pattern repeat

⑤ and you get the $\ell$: length per strip

Quick example

With an 8 ft (96 in) ceiling, a 4 in trim allowance and a 21 in pattern repeat, the length per strip is

strip length $\ell$ $=$ repeat (21 in) $\times$ $\lceil$ $($ ceiling height (96 in) $+$ trim (4 in) $)$ $\div$ repeat (21 in) $\rceil$

$(96 + 4) \div 21 = 100 \div 21 \approx 4.76$

$\lceil 4.76 \rceil = 5$

$21 \times 5 = 105\,\mathrm{in} = 8.75\,\mathrm{ft}$

Key idea

Wallpaper is hung in vertical strips from the ceiling to the floor. Besides the ceiling height, each strip needs a little extra to trim at the top and bottom (about 2 in at each end, 4 in in total), so for plain paper one strip is $H + m$ (100 in in the example). For patterned paper, every strip has to start at the same point in the pattern so that it lines up with the strip next to it. When you cut strip after strip from a roll, the next strip starts at the same point only if each strip is a whole number of repeats long. So divide $H + m$ by the repeat, round up and multiply back. In the example, 100 in becomes 105 in: 5 in extra per strip for pattern matching. The larger the repeat (such as 21 or 25 in), the bigger this difference. Wallpaper with a "drop match" (half-drop), where the pattern repeats shifted by half, may need more than this calculation. Follow the product label.

Strips needed

Figure

Standard notation (the usual math form)

$n$ $=$ $\lceil$ $A$ $\div$ $($ $W$ $\times$ $H$ $)$ $\rceil$

In words (symbols replaced with words)

④ $n$: strips needed $=$ $\lceil$ ① $A$: net wall area $\div$ $($ ② $W$: wallpaper width $\times$ ③ $H$: ceiling height $)$ $\rceil$

The formula in words

① Take the $A$: net wall area

② divide it by the area one strip covers, the $W$: wallpaper width

③ times the $H$: ceiling height and round up

④ and you get the $n$: strips needed

Quick example

To cover the 319 ft² net wall area above with 20.5 in wide paper and an 8 ft ceiling, the number of strips is

strips $n$ $=$ $\lceil$ net area (319 ft²) $\div$ $($ width (20.5/12 ft) $\times$ ceiling height (8 ft) $)$ $\rceil$

$\tfrac{20.5}{12} \times 8 \approx 13.67\,\mathrm{ft^2}$

$319 \div 13.67 \approx 23.34$

$\lceil 23.34 \rceil = 24$

Key idea

The idea is to divide the net area by how much wall one strip (width $W$, height $H$) covers. With no openings, $A = L \times H$, so the formula is the same as $\lceil L \div W \rceil$ (perimeter ÷ paper width, rounded up). In the example, without subtracting openings it would be $\lceil 44 \times 12 \div 20.5 \rceil = \lceil 25.76 \rceil = 26$ strips; with the openings subtracted it is 24. You find the number of strips first and then multiply by the strip length because the rounding up for the pattern happens strip by strip. If you calculate by area alone, that rounding (the pattern matching waste) is left out. Subtracting openings to reduce the strip count assumes that the short pieces above and below windows and above doors are cut from leftover pieces (the same way a contractor's square footage works). With patterned paper, leftovers can be reused only if the pattern lines up, so for patterned paper or if it is your first time, leave the openings blank and use $\lceil L \div W \rceil$ (perimeter ÷ width) to be on the safe side.

Length needed with waste

Standard notation (the usual math form)

$M$ $=$ $n$ $\times$ $\ell$ $\times$ $($ $1$ $+$ $\rho$ $)$

In words (symbols replaced with words)

④ $M$: length with waste $=$ ① $n$: strips needed $\times$ ② $\ell$: length per strip $\times$ $($ $1$ $+$ ③ $\rho$: waste rate $)$

The formula in words

① Take the $n$: strips needed

② multiply it by the $\ell$: length per strip to get the length before waste

③ multiply by "1 + $\rho$: waste rate " (1.1 for 10%)

④ and you get the $M$: length with waste

Quick example

With 24 strips of 8.75 ft and 10% waste, the length you need is

with waste $M$ $=$ strips (24) $\times$ strip length (8.75 ft) $\times$ $($ $1$ $+$ waste (0.1) $)$

$24 \times 8.75 = 210\,\mathrm{ft}$

$210 \times (1 + 0.1) = 210 \times 1.1 = 231\,\mathrm{ft}$

Key idea

The waste percentage is extra for cut-outs around outlets and windows, mistakes and spares for future repairs. The pattern matching was already covered strip by strip in the earlier formula, so this covers only the rest. About 10% even for plain paper, and 15-20% for patterned paper or first-timers, are common; there is no single right value. If you run short, you may not be able to get paper from the same production run (dye lot), and the color may not match, so it is safer to buy more. If you buy paper cut to length, $M$ rounded up is the length to order.

Rolls needed

Standard notation (the usual math form)

$B$ $=$ $\lceil$ $M$ $\div$ $K$ $\rceil$

In words (symbols replaced with words)

③ $B$: rolls needed $=$ $\lceil$ ① $M$: length with waste $\div$ ② $K$: roll length $\rceil$

The formula in words

① Take the $M$: length with waste

② divide it by the $K$: roll length and round up

③ and you get the $B$: rolls needed

Quick example

When you need 231 ft of wallpaper with waste and it comes in 33 ft double rolls, the number of rolls is

rolls $B$ $=$ $\lceil$ length (231 ft) $\div$ roll length (33 ft) $\rceil$

$231 \div 33 = 7$

$\lceil 7 \rceil = 7$

Key idea

You can only buy whole rolls, so if the division leaves a decimal, always round up. Rounding down or to the nearest whole number would leave you short. But one roll gives only $\lfloor K \div \ell \rfloor$ strips (rounded down). A 33 ft double roll with 8.75 ft strips gives 3 strips (the last 6.75 ft is too short for a strip), so 24 strips need $\lceil 24 \div 3 \rceil = 8$ rolls, one more than the 7 rolls you get from the length alone. With 7 rolls (21 strips) you would be 3 strips short. With 16.5 ft single rolls, each roll gives only 1 strip of 8.75 ft, so you would need 24 single rolls, far more than the 14 the length suggests. That is why double rolls are the better buy for tall walls and large repeats. This calculator works out both "rolls by length" and "rolls by strips per roll" and uses the larger number.

Estimated cost

Standard notation (the usual math form)

In words (symbols replaced with words)

$T$ $=$ $u$ $\times$ $Q$

③ $T$: estimated cost $=$ ① $u$: unit price $\times$ ② $Q$: quantity

The formula in words

① Take the $u$: unit price (per ft, per roll or per ft²)

② multiply it by the $Q$: quantity (length, rolls or area, to match the unit price)

③ and you get the $T$: estimated cost

Quick example

The cost of 8 double rolls at $45 per roll is

estimated cost $T$ $=$ unit price ($45 per roll) $\times$ quantity (8 rolls)

$45 \times 8 = 360$

Key idea

The key is to match the unit of the price and the quantity. For a price per foot, multiply by the length with waste $M$; for a price per roll, by the number of rolls $B$; for a price per square foot (such as an installed price), by the net wall area $A$. Many US wallpapers are priced per single roll but sold only in double rolls, so check which one the price refers to. Paste, primer, surface preparation and tools cost extra on top of the paper itself.

To find how much wallpaper you need, divide the net wall area (without openings) by the area one strip covers (width × ceiling height) and round up to get the number of strips. Multiply by the length per strip (ceiling height + trim, rounded up to a whole number of pattern repeats) and add the waste percentage. Patterned paper rounds up strip by strip, so the same length as plain paper will not be enough. Finally, check how many strips one roll really gives.

Symbols and terms

Symbols

$L$	ell	The room perimeter (the total width of the walls). If you enter length × width, $L = 2 \times (\text{length} + \text{width})$. $L$ is from "length".
$H$	aitch	The ceiling height (from the floor to the ceiling), from "height".
$D$	dee	The total area of the openings (doors, windows and other parts you do not paper) - width × height × count for each size, added up. Think of it as "D for door".
$A$	ay	The net wall area. It is found with $A = L \times H - D$ (plus any extra area). $A$ is from "area".
$W$	double-u	The wallpaper width. Standard US double rolls are 20.5 in wide. $W$ is from "width".
$R$	ar	The pattern repeat (the vertical length after which the pattern repeats). Plain paper counts as 0. $R$ is from "repeat".
$m$	em	The trim allowance at the top and bottom, added together - the extra length for trimming at the ceiling and the floor. About 2 in at each end (4 in in total) is typical. $m$ is from "margin".
$\ell$	script ell	The length per strip. It is found with $\ell = R \times \lceil (H + m) \div R \rceil$ ($H + m$ for plain paper). A script lowercase letter is used to tell it apart from the perimeter $L$.
$n$	en	The number of strips needed. It is found with $n = \lceil A \div (W \times H) \rceil$. $n$ is from "number".
$\rho$	rho	The waste rate. For 10%, $\rho = 0.1$ and you multiply by $1 + \rho = 1.1$. It is a Greek letter often used for rates and ratios.
$M$	capital em	The length needed with waste. It is found with $M = n \times \ell \times (1 + \rho)$.
$K$	kay	The length of one roll. A US double roll is 33 ft and a single roll 16.5 ft.
$B$	bee	The number of rolls needed. It is found with $B = \lceil M \div K \rceil$, but if dividing the strips needed $n$ by the strips per roll $\lfloor K \div \ell \rfloor$ and rounding up gives more rolls, that number is used.
$u$	you	The unit price of the wallpaper (per foot, per roll or per square foot), from "unit price".
$Q$	cue	The quantity that matches the unit of the price (length, number of rolls or area), from "quantity".
$T$	tee	The estimated cost (paper only; paste and surface preparation are not included), from "total".
$\lceil x \rceil$	ceiling of x	The symbol for rounding up to a whole number (the ceiling function). (Example - $\lceil 23.34 \rceil = 24$, $\lceil 5 \rceil = 5$)
$\lfloor x \rfloor$	floor of x	The symbol for rounding down to a whole number (the floor function). It is used when a leftover that is too short does not count, as in the strips per roll $\lfloor K \div \ell \rfloor$. (Example - $\lfloor 3.77 \rfloor = 3$)

Terms

wallpaper	A sheet material of a set width used to finish walls and ceilings. In the US it is usually sold in double rolls 20.5 in wide and 33 ft long (about 56 ft²), often priced per single roll (16.5 ft). Some papers are 27 in wide or other widths.
perimeter	The total length of the walls around the room. For a rectangular room, (length + width) × 2. Wallpaper is hung vertically, so the perimeter divided by the paper width tells you how many strips fit side by side.
opening	A part of the wall that gets no wallpaper, such as a door, a window or a closet door. Find its area as width × height × count and subtract it from the wall area. Some people leave small windows in as extra margin.
net wall area	The total wall area (perimeter × ceiling height) minus the openings - the area you actually paper. The square footage in a contractor's quote for wallpaper usually means this area.
pattern repeat	The vertical length after which the pattern repeats, shown on the label as, for example, "pattern repeat 21 in". To line up the pattern with the next strip, each strip is cut to a multiple of this length, and what is left over is the pattern matching waste.
pattern matching	Hanging strips so that the pattern flows from one strip to the next. Paper that needs matching is rounded up by the repeat on every strip, so it needs more length than plain paper.
trim allowance	The extra length beyond the ceiling height that you leave to trim at the ceiling and the floor. About 2 in at each end, 4 in in total, is typical.
waste percentage	The percentage added to the calculated amount for cut-outs, mistakes and spares. About 10% for plain paper and 15-20% for patterned paper or first-timers are common; there is no single right value.
rounding up	Raising a number with a decimal part to the next whole number. Wallpaper comes only in whole strips and rolls, so counts are always rounded up.
double roll	The usual way wallpaper is packaged in the US - one continuous roll that is twice as long as a single roll (about 33 ft instead of 16.5 ft for 20.5 in wide paper). A longer roll gives more full-length strips per roll and less waste.
accent wall	Papering or painting just one wall of a room in a different color or pattern. On this page, choose "Perimeter" and enter only that wall's width to get the amount for one wall.

Good to know before you start

Here is what helps you use the calculation on this page with real understanding, not just by pressing the button.

Area and perimeter of a rectangle (Grade 3)	Knowing that the area of a rectangle is length × width Knowing that the perimeter of a rectangle is (length + width) × 2
Converting units of length (Grades 4–5)	Knowing that 1 ft = 12 in, so you can turn 96 in into 8 ft and 20.5 in into 20.5/12 ft
Multiplying and dividing decimals (Grades 5–6)	Understanding what decimal calculations such as $24 \times 8.75$ and $319 \div 13.67$ mean (a calculator can do the arithmetic)
Percents (Grade 6)	Knowing that "10% more" can be calculated as "× 1.1"
Rounding (Grades 3–4)	Knowing the difference between rounding up, rounding down and rounding to the nearest whole number Being able to explain in your own words why the number of strips and rolls is always rounded up
Multiples (Grade 4)	Seeing that the smallest multiple of 21 that is at least 100 is 105 (the idea behind rounding up by the pattern repeat)

How to calculate it in Excel

Copy the whole table below and paste it into cell A1 in Excel. It works as is.

Table to find the net wall area

Room length (ft)	12
Room width (ft)	10
Ceiling height (ft)	8
Total area of openings (ft²)	33
Room perimeter (ft)	=2*(B1+B2)
Net wall area (ft²)	=B5*B3-B4

Table to find the length per strip

Ceiling height (in)	96
Trim allowance (in)	4
Pattern repeat (in, 0 if plain)	21
Length per strip (in)	=IF(B3>0,B3*ROUNDUP((B1+B2)/B3,0),B1+B2)

Table to find the strips needed

Net wall area (ft²)	319
Wallpaper width (in)	20.5
Ceiling height (ft)	8
Strips needed	=ROUNDUP(B1/(B2/12*B3),0)

Table to find the length needed with waste

Strips needed	24
Length per strip (ft)	8.75
Waste (%)	10
Length with waste (ft)	=B1B2(1+B3/100)

Table to find the rolls needed

Length with waste (ft)	231
Roll length (ft)	33
Strips needed	24
Length per strip (ft)	8.75
Strips per roll	=INT(B2/B4)
Rolls needed	=MAX(ROUNDUP(B1/B2,0),ROUNDUP(B3/B5,0))

Table to find the estimated cost

Unit price ($)	45
Quantity (ft, rolls or ft²)	8
Estimated cost ($)	=B1*B2

After pasting, the upper rows of column B are your inputs and the last row is calculated automatically.
"ROUNDUP(value, 0)" rounds up to a whole number (the ⌈ ⌉ in the formulas), and "INT(value)" rounds down (the ⌊ ⌋ in the formulas).
The second table works in inches and uses the IF function so that it rounds up to a multiple of the repeat only when the repeat (B3) is greater than 0; for plain paper (0) it uses ceiling height + trim as is. The third table turns the paper width into feet with "/12".
The fifth table uses the MAX function to take the larger of the rolls by length (B1 ÷ B2 rounded up) and the rolls by strips per roll (B3 ÷ B5 rounded up).
B6 in the first table is 319, B4 in the second is 105 in (8.75 ft), B4 in the third is 24 strips, B4 in the fourth is 231, B5 and B6 in the fifth are 3 strips and 8 rolls, and B3 in the sixth is 360. Just replace the numbers in column B with your own.

How to calculate it in Google Sheets

Copy the whole table below and paste it into cell A1 in Google Sheets. It works as is.

Table to find the net wall area

Room length (ft)	12
Room width (ft)	10
Ceiling height (ft)	8
Total area of openings (ft²)	33
Room perimeter (ft)	=2*(B1+B2)
Net wall area (ft²)	=B5*B3-B4

Table to find the length per strip

Ceiling height (in)	96
Trim allowance (in)	4
Pattern repeat (in, 0 if plain)	21
Length per strip (in)	=IF(B3>0,B3*ROUNDUP((B1+B2)/B3,0),B1+B2)

Table to find the strips needed

Net wall area (ft²)	319
Wallpaper width (in)	20.5
Ceiling height (ft)	8
Strips needed	=ROUNDUP(B1/(B2/12*B3),0)

Table to find the length needed with waste

Strips needed	24
Length per strip (ft)	8.75
Waste (%)	10
Length with waste (ft)	=B1B2(1+B3/100)

Table to find the rolls needed

Length with waste (ft)	231
Roll length (ft)	33
Strips needed	24
Length per strip (ft)	8.75
Strips per roll	=INT(B2/B4)
Rolls needed	=MAX(ROUNDUP(B1/B2,0),ROUNDUP(B3/B5,0))

Table to find the estimated cost

Unit price ($)	45
Quantity (ft, rolls or ft²)	8
Estimated cost ($)	=B1*B2

The same formulas as in Excel (including the ROUNDUP, INT, MAX and IF functions) work as is. Copy the whole table, paste it into cell A1, and replace the numbers in column B with your own.

How to calculate it in Python

import math

room_length_ft = 12       # room length (ft)
room_width_ft = 10        # room width (ft)
ceiling_height_ft = 8     # ceiling height (ft)
openings = [              # openings (width ft, height ft, count). Use [] if none
    (3, 7, 1),            # door
    (3, 4, 1),            # window
]
paper_width_in = 20.5     # wallpaper width (in)
repeat_in = 21            # pattern repeat (in). 0 for plain paper
margin_in = 4             # trim allowance, top + bottom (in)
loss_rate = 0.10          # waste rate (0.10 for 10%)
roll_length_ft = 33       # roll length (ft). US double roll = 33 ft
price_per_roll = 45       # price per roll ($)

# net wall area A = perimeter x ceiling height - total area of openings
perimeter_ft = 2 * (room_length_ft + room_width_ft)
openings_area_ft2 = sum(w * h * count for w, h, count in openings)
net_area_ft2 = perimeter_ft * ceiling_height_ft - openings_area_ft2

# length per strip (rounded up to a multiple of the repeat; plain paper = ceiling height + trim)
need_len_in = ceiling_height_ft * 12 + margin_in
if repeat_in > 0:
    strip_length_in = repeat_in * math.ceil(need_len_in / repeat_in)
else:
    strip_length_in = need_len_in
strip_length_ft = strip_length_in / 12

strips = math.ceil(net_area_ft2 / (paper_width_in / 12 * ceiling_height_ft))  # strips needed (round up)
length_net_ft = strips * strip_length_ft                                      # length before waste
length_total_ft = length_net_ft * (1 + loss_rate)                             # length with waste
rolls_by_length = math.ceil(round(length_total_ft, 2) / roll_length_ft)       # rolls by length (round up)
strips_per_roll = math.floor(roll_length_ft / strip_length_ft)                # strips per roll (round down)
rolls_by_strips = math.ceil(strips / strips_per_roll)                         # rolls by strips (round up)
rolls = max(rolls_by_length, rolls_by_strips)                                 # rolls needed (the larger)
cost = rolls * price_per_roll                                                 # estimated cost ($)

print(f"Room perimeter: {perimeter_ft:.3f} ft")
print(f"Net wall area: {net_area_ft2:.2f} ft²")
print(f"Length per strip: {strip_length_ft:.3f} ft")
print(f"Strips needed: {strips}")
print(f"Length with waste: {length_total_ft:.2f} ft")
print(f"Strips per roll: {strips_per_roll}")
print(f"Rolls needed: {rolls}")
print(f"Estimated cost: ${cost:,.2f}")

Runs with the standard library only. math.ceil() rounds up (the ⌈ ⌉ in the formulas) and math.floor() rounds down (the ⌊ ⌋). The rolls needed are the larger of the rolls by length and the rolls by strips per roll, chosen with max(). Replace the room size, openings, wallpaper details and price at the top with your own and run it. With no openings, use openings = [].

How to write it in LaTeX and other math languages (copy and paste)

Net wall area (the area minus openings)

A = L × H − D

A = L H - D

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>A</mi>
    <mo>=</mo>
    <mi>L</mi>
    <mo>&#xD7;</mo>
    <mi>H</mi>
    <mo>&#x2212;</mo>
    <mi>D</mi>
  </mrow>
</math>

A = L * H - D

l*h - d

A := L*H - Dop;

A = L*H - D;

A = L × H − D

Length per strip (with pattern match and trim allowance)

ℓ = R × ⌈(H + m) ÷ R⌉

\ell = R \left\lceil \frac{H + m}{R} \right\rceil

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>&#x2113;</mi>
    <mo>=</mo>
    <mi>R</mi>
    <mo>&#x2308;</mo>
    <mfrac><mrow><mi>H</mi><mo>+</mo><mi>m</mi></mrow><mi>R</mi></mfrac>
    <mo>&#x2309;</mo>
  </mrow>
</math>

l = R |~ (H + m) / R ~|

r*Ceiling[(h + m)/r]

l := R*ceil((H + m)/R);

l = R*ceil((H + m)/R);

ℓ = R⌈(H + m)/R⌉

Strips needed

n = ⌈A ÷ (W × H)⌉

n = \left\lceil \frac{A}{W H} \right\rceil

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>n</mi>
    <mo>=</mo>
    <mo>&#x2308;</mo>
    <mfrac><mi>A</mi><mrow><mi>W</mi><mi>H</mi></mrow></mfrac>
    <mo>&#x2309;</mo>
  </mrow>
</math>

n = |~ A / (W * H) ~|

Ceiling[a/(w*h)]

n := ceil(A/(W*H));

n = ceil(A/(W*H));

n = ⌈A/(W H)⌉

Length needed with waste

M = n × ℓ × (1 + ρ)

M = n \ell (1 + \rho)

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>M</mi>
    <mo>=</mo>
    <mi>n</mi>
    <mo>&#x2062;</mo>
    <mi>&#x2113;</mi>
    <mo>&#x2062;</mo>
    <mrow><mo>(</mo><mn>1</mn><mo>+</mo><mi>&#x3C1;</mi><mo>)</mo></mrow>
  </mrow>
</math>

M = n * l * (1 + rho)

n*l*(1 + rho)

M := n*l*(1 + rho);

M = n*l*(1 + rho);

M = n ℓ (1 + ρ)

Rolls needed

B = ⌈M ÷ K⌉

B = \left\lceil \frac{M}{K} \right\rceil

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>B</mi>
    <mo>=</mo>
    <mo>&#x2308;</mo>
    <mfrac><mi>M</mi><mi>K</mi></mfrac>
    <mo>&#x2309;</mo>
  </mrow>
</math>

B = |~ M / K ~|

Ceiling[m/k]

B := ceil(M/K);

B = ceil(M/K);

B = ⌈M/K⌉

Estimated cost

T = u × Q

T = u \times Q

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>T</mi>
    <mo>=</mo>
    <mi>u</mi>
    <mo>&#xD7;</mo>
    <mi>Q</mi>
  </mrow>
</math>

T = u * Q

u*q

T := u*Q;

T = u*Q;

T = u × Q

How to have ChatGPT do the calculation

You are a quantity calculation assistant for interior work. Do the following calculation by actually running Python code, and base your answer only on the numbers from the execution result (do not answer by mental math or guessing).

I am wallpapering a room that is 12 ft long and 10 ft wide, with an 8 ft ceiling. There is one door (3 ft × 7 ft) and one window (3 ft × 4 ft).
The wallpaper is 20.5 inches wide with a 21-inch pattern repeat. The trim allowance is 4 inches in total, and the waste rate is 10%.
Find each of the following:
1. The room perimeter and the net wall area without the openings (ft²)
2. The length per strip (ceiling height + trim, rounded up to a multiple of the pattern repeat)
3. The number of strips (net area ÷ (paper width × ceiling height), rounded up)
4. The length needed with waste (strips × strip length × 1.1)
5. The number of 33-foot double rolls needed (the larger of: length ÷ 33 rounded up, and strips ÷ "strips per roll (33 ÷ strip length, rounded down)" rounded up)

Show the formulas you used and the numbers from the execution result.

How to Use

1

Enter your numbers

Type the numbers you want to calculate with into the input fields
2

Calculate

Press the "Calculate" button
3

Check the result

The result appears on the spot. The same page also explains the idea behind the calculation and the formula

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\(L\)	ell	The room perimeter (the total width of the walls). If you enter length × width, \(L = 2 \times (\text{length} + \text{width})\). \(L\) is from "length".
\(H\)	aitch	The ceiling height (from the floor to the ceiling), from "height".
\(D\)	dee	The total area of the openings (doors, windows and other parts you do not paper) - width × height × count for each size, added up. Think of it as "D for door".
\(A\)	ay	The net wall area. It is found with \(A = L \times H - D\) (plus any extra area). \(A\) is from "area".
\(W\)	double-u	The wallpaper width. Standard US double rolls are 20.5 in wide. \(W\) is from "width".
\(R\)	ar	The pattern repeat (the vertical length after which the pattern repeats). Plain paper counts as 0. \(R\) is from "repeat".
\(m\)	em	The trim allowance at the top and bottom, added together - the extra length for trimming at the ceiling and the floor. About 2 in at each end (4 in in total) is typical. \(m\) is from "margin".
\(\ell\)	script ell	The length per strip. It is found with \(\ell = R \times \lceil (H + m) \div R \rceil\) (\(H + m\) for plain paper). A script lowercase letter is used to tell it apart from the perimeter \(L\).
\(n\)	en	The number of strips needed. It is found with \(n = \lceil A \div (W \times H) \rceil\). \(n\) is from "number".
\(\rho\)	rho	The waste rate. For 10%, \(\rho = 0.1\) and you multiply by \(1 + \rho = 1.1\). It is a Greek letter often used for rates and ratios.
\(M\)	capital em	The length needed with waste. It is found with \(M = n \times \ell \times (1 + \rho)\).
\(K\)	kay	The length of one roll. A US double roll is 33 ft and a single roll 16.5 ft.
\(B\)	bee	The number of rolls needed. It is found with \(B = \lceil M \div K \rceil\), but if dividing the strips needed \(n\) by the strips per roll \(\lfloor K \div \ell \rfloor\) and rounding up gives more rolls, that number is used.
\(u\)	you	The unit price of the wallpaper (per foot, per roll or per square foot), from "unit price".
\(Q\)	cue	The quantity that matches the unit of the price (length, number of rolls or area), from "quantity".
\(T\)	tee	The estimated cost (paper only; paste and surface preparation are not included), from "total".
\(\lceil x \rceil\)	ceiling of x	The symbol for rounding up to a whole number (the ceiling function). (Example - \(\lceil 23.34 \rceil = 24\), \(\lceil 5 \rceil = 5\))
\(\lfloor x \rfloor\)	floor of x	The symbol for rounding down to a whole number (the floor function). It is used when a leftover that is too short does not count, as in the strips per roll \(\lfloor K \div \ell \rfloor\). (Example - \(\lfloor 3.77 \rfloor = 3\))

Wallpaper Calculator (How Many Rolls, with Pattern Repeat and Waste)

Table of Contents

What you can do on this page

What is this calculation used for?

Formulas and figures

Symbols and terms

Symbols

Terms

Good to know before you start

How to calculate it in Excel

How to calculate it in Google Sheets

How to calculate it in Python

How to write it in LaTeX and other math languages (copy and paste)

How to have ChatGPT do the calculation

How to Use

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