Concrete Calculator (Cubic Yards, Weight and Bags)

Choose the shape you are building, then enter the dimensions and the density of the concrete.

Units

Shape

Length

Width

Thickness (height)

Quantity

Concrete density (t/m³)

Extra for waste

Choose mm, cm or m for each dimension. Everything is converted to meters for the calculation.

Result and figure

Choose a shape in the fields on the left, enter the dimensions and press "Calculate". The result will appear here.

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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

Switch between five shapes (slab or wall, column or hole, circular slab or tube, curb and gutter, and stairs) and get the volume of concrete in cubic feet and cubic yards on the spot
The weight (volume × density) is shown in pounds and tons. You can change the density; 144 lb/ft³ for plain concrete and 150 lb/ft³ for reinforced concrete are common values
The result shows how many bags of concrete mix you need, rounded up, for the 80, 60 and 40 lb bags sold at US home improvement stores
You can add 5% or 10% extra for waste from spills, forms that bulge and concrete soaking into the ground
A plain-language explanation of the formulas and copy-and-paste formulas for Excel, Google Sheets and Python are all on this page

The volume, weight and number of bags are estimates. The density depends on the aggregate and the mix, and the yield of a bag differs by brand, so check the bag label and your contractor's estimate too. By default this page works in inches, feet and yards; switch "Units" above the calculator to Metric to use mm, cm, m and 25 kg bags.

What is this calculation used for?

DIY slab for a parking pad or shed

For example, a slab for one parking space (20 × 10 ft), 4 in thick, is \(20 \times 10 \times \tfrac{4}{12} \approx 66.67\) ft³, or about 2.47 yd³. It weighs \(66.67 \times 144 = 9600\) lb (4.8 tons), and would take 112 bags of 80 lb mix.
That tells you before you shop that mixing bags by hand is not realistic, so you can decide between ordering a ready-mix truck and doing it with bags.

Setting fence or deck posts (filling holes)

A post hole 10 in across and 24 in deep takes \(\pi \times (5/12)^2 \times 2 \approx 1.09\) ft³, so about 2 bags of 80 lb mix per hole. Ten posts take about 10.9 ft³, about 1,570 lb, or 19 bags of 80 lb.
Knowing "about 2 bags per post" in advance saves extra trips to the store and leftover bags.

How much ready-mix to order from a truck

Ready-mix concrete is ordered by the cubic yard, and many suppliers take orders in steps of 1/4 or 1/2 yd³. If your volume is 2.47 yd³, adding 5-10% for waste gives 2.59 to 2.72 yd³, so you would order about 2.75 yd³.
Small orders often carry a short-load fee, so calculating the volume first is the starting point for comparing quotes.

Quantity takeoff for site and civil work

For structures with the same cross-section along their length, such as a curb and gutter, you find the cross-sectional area from the drawing and multiply by the length. This is the same idea as a "quantity takeoff" in construction estimating.
A curb and gutter with a 6 in × 6 in curb and an 18 in wide, 6 in thick flag has a cross-section of \(0.5 \times 1 + 1.5 \times 0.5 = 1.25\) ft², so 100 ft takes 125 ft³ (about 4.63 yd³). The amount grows in step with the length.

Pouring front entry steps

For three steps in front of the house with an 11 in tread, a 7 in riser and a width of 48 in (no landing), the cross-section is \(\tfrac{11 \times 7}{144} \times 3 \approx 1.604\) ft² and the volume is \(1.604 \times 4 \approx 6.42\) ft³. That is about 924 lb, or 11 bags of 80 lb mix.
Steps are more solid than they look, so working out the volume with the formula keeps you from buying too much or too little.

Formulas and figures

Volume of a slab, wall or square footing

Figure

Standard notation (the usual math form)

\(V\) \(=\) \(l\) \(\times\) \(w\) \(\times\) \(h\) \(\times\) \(q\)

In words (symbols replaced with words)

⑤ \(V\): volume \(=\) ① \(l\): length \(\times\) ② \(w\): width \(\times\) ③ \(h\): thickness (height) \(\times\) ④ \(q\): quantity

The formula in words

① Take the \(l\): length

② multiply it by the \(w\): width to get the base area

③ multiply by the \(h\): thickness (height) to get the volume of one piece

④ multiply by the \(q\): quantity

⑤ and you get the \(V\): volume

Quick example

For one 9 × 9 ft patio slab, 4 in (1/3 ft) thick, the volume of concrete is

volume \(V\) \(=\) length (9 ft) \(\times\) width (9 ft) \(\times\) thickness (1/3 ft) \(\times\) quantity (1)

\(9 \times 9 \times \tfrac{4}{12} \times 1 = 27\,\mathrm{ft^3}\)

\(27 \div 27 = 1\,\mathrm{yd^3}\)

Key idea

This is the same formula as the volume of a box: length × width × height. Before calculating, always turn inches into feet (4 in = 4 ÷ 12 = 1/3 ft). For a wall, read it as "length × height × thickness" and the same formula works. Ready-mix concrete is sold by the cubic yard. Since 1 yd³ = 3 × 3 × 3 = 27 ft³, divide cubic feet by 27 to get cubic yards.

Volume of a column, hole or round footing

Figure

Standard notation (the usual math form)

\(V\) \(=\) \(\pi\) \(\times\) \(\left(\dfrac{d}{2}\right)^{2}\) \(\times\) \(h\) \(\times\) \(q\)

In words (symbols replaced with words)

⑤ \(V\): volume \(=\) ② \(\pi\): pi \(\times\) ① radius (diameter \(d\) ÷ 2) squared \(\times\) ③ \(h\): depth (height) \(\times\) ④ \(q\): quantity

The formula in words

① Take the radius (diameter \(d\) ÷ 2) squared

② multiply it by \(\pi\): pi (about 3.14) to get the area of the circle (the base)

③ multiply by the \(h\): depth (height) to get the volume of one

④ multiply by the \(q\): quantity

⑤ and you get the \(V\): volume

Quick example

To fill one fence post hole 10 in across and 24 in (2 ft) deep, the volume of concrete is

volume \(V\) \(=\) pi (about 3.14) \(\times\) radius squared ((5/12)²) \(\times\) depth (2 ft) \(\times\) quantity (1)

\(3.14159\ldots \times \left(\tfrac{5}{12}\right)^{2} \times 2 \times 1 = 3.14159\ldots \times 0.17361\ldots \times 2 \approx 1.091\,\mathrm{ft^3}\)

Key idea

This is the same formula as the volume of a cylinder: base area (radius × radius × pi) × height. You enter the diameter, not the radius, so the key is to divide by 2 before squaring (a 10 in diameter is a 5 in radius, 5/12 ft). The same formula works for pouring into a hole in the ground and for a column that stands above ground. For a fence post, the post itself takes up some of the hole (a 4×4 post, 3.5 × 3.5 in, takes about 0.17 ft³ in a 2 ft hole), so this volume is slightly on the safe side.

Volume of a circular slab or tube

Figure

Standard notation (the usual math form)

\(V\) \(=\) \(\pi\) \(\times\) \((\) \(\left(\dfrac{d_{1}}{2}\right)^{2}\) \(-\) \(\left(\dfrac{d_{2}}{2}\right)^{2}\) \()\) \(\times\) \(h\) \(\times\) \(q\)

In words (symbols replaced with words)

⑥ \(V\): volume \(=\) ③ \(\pi\): pi \(\times\) \((\) ① outer radius (\(d_{1}\) ÷ 2) squared \(-\) ② inner radius (\(d_{2}\) ÷ 2) squared \()\) \(\times\) ④ \(h\): height (length) \(\times\) ⑤ \(q\): quantity

The formula in words

① From the outer radius (\(d_{1}\) ÷ 2) squared

② subtract the inner radius (\(d_{2}\) ÷ 2) squared

③ multiply by \(\pi\): pi to get the area of the ring

④ multiply by the \(h\): height (length)

⑤ multiply by the \(q\): quantity

⑥ and you get the \(V\): volume

Quick example

For one ring-shaped slab with an outer diameter of 10 ft, an inner diameter of 6 ft and a thickness of 4 in (1/3 ft), the volume is

volume \(V\) \(=\) pi (about 3.14) \(\times\) \((\) outer radius squared (5²) \(-\) inner radius squared (3²) \()\) \(\times\) thickness (1/3 ft)

\(3.14159\ldots \times (5^{2} - 3^{2}) \times \tfrac{1}{3} = 3.14159\ldots \times 16 \div 3 \approx 16.76\,\mathrm{ft^3}\)

Key idea

This combines "the volume of the outer cylinder minus the volume of the hollow inner cylinder" into one formula. Enter 0 for the inner diameter \(d_{2}\) and it becomes the formula for an ordinary solid round slab. Use it for any shape with a ring-shaped cross-section, such as a collar around a manhole, a ring around a tree or the edge of a round flower bed. For a pipe lying on its side, read \(h\) as the length of the pipe and the formula is the same.

Volume of a curb and gutter

Figure

Standard notation (the usual math form)

\(V\) \(=\) \(\{\) \(b\) \(\times\) \((\) \(h\) \(+\) \(f\) \()\) \(+\) \(g\) \(\times\) \(f\) \(\}\) \(\times\) \(l\)

In words (symbols replaced with words)

⑥ \(V\): volume \(=\) \(\{\) ① \(b\): curb depth \(\times\) \((\) ② \(h\): curb height \(+\) ③ \(f\): gutter flag thickness \()\) \(+\) ④ \(g\): gutter width \(\times\) \(f\): gutter flag thickness \(\}\) \(\times\) ⑤ \(l\): length

The formula in words

① Take the \(b\): curb depth

② multiply it by the sum of the \(h\): curb height

③ and the \(f\): gutter flag thickness to get the cross-section of the curb part

④ add the \(g\): gutter width × the same flag thickness \(f\) (the cross-section of the gutter part)

⑤ multiply by the \(l\): length

⑥ and you get the \(V\): volume

Quick example

For a curb and gutter with a curb 6 in deep and 6 in high, a 6 in thick gutter flag 12 in wide, and a length of 30 ft (quantity 1), the volume is

\(0.5 \times (0.5 + 0.5) + 1 \times 0.5 = 0.5 + 0.5 = 1\,\mathrm{ft^2}\)

\(1 \times 30 = 30\,\mathrm{ft^3} \approx 1.11\,\mathrm{yd^3}\)

Key idea

For structures like a curb and gutter, where the same cross-section continues along the length, the volume is "cross-sectional area × length". This formula splits the L-shaped cross-section into two rectangles (the upright curb part and the flat gutter part at its foot) and adds their areas. Note that the height of the curb part includes the flag thickness \(f\), so it is \(h + f\). To build several of the same thing, multiply the volume by the quantity (the "Quantity" field of the calculator).

Volume of concrete stairs

Figure

Standard notation (the usual math form)

\(V\) \(=\) \((\) \(t\) \(\times\) \(r\) \(\times\) \(\dfrac{n(n-1)}{2}\) \(+\) \(p\) \(\times\) \(n\) \(\times\) \(r\) \()\) \(\times\) \(w\)

In words (symbols replaced with words)

⑥ \(V\): volume \(=\) \((\) ① \(t\): tread depth \(\times\) ② \(r\): riser height \(\times\) ③ stacked steps \(\dfrac{n(n-1)}{2}\) \(+\) ④ \(p\): platform depth \(\times\) \(n\): number of steps \(\times\) \(r\): riser height \()\) \(\times\) ⑤ \(w\): stair width

The formula in words

① Take the \(t\): tread depth

② multiply it by the \(r\): riser height to get the area of one step's rectangle

③ multiply by the stacked steps \(\dfrac{n(n-1)}{2}\) (\(= 1 + 2 + \cdots + (n-1)\) rectangles stacked up) to get the cross-section of the stepped part

④ add the rectangle under the platform, \(p\): platform depth × number of steps \(n\) × riser height \(r\)

⑤ multiply by the \(w\): stair width

⑥ and you get the \(V\): volume

Quick example

For porch steps with an 11 in tread, a 7 in riser, 3 steps, a 36 in deep platform (landing) and a width of 36 in (3 ft), the volume is

\(\tfrac{11}{12} \times \tfrac{7}{12} \times \dfrac{3 \times 2}{2} + 3 \times 3 \times \tfrac{7}{12} \approx 1.604 + 5.25 = 6.854\,\mathrm{ft^2}\)

\(6.854 \times 3 \approx 20.56\,\mathrm{ft^3} \approx 0.76\,\mathrm{yd^3}\)

Key idea

If you slice solid stairs into thin vertical strips, there is one riser's worth of rectangle under the first tread, two under the second, and so on, and \(n-1\) under the last tread before the platform. \(\dfrac{n(n-1)}{2}\) adds up \(1+2+\cdots+(n-1)\). Under the platform there is one large rectangle, "depth \(p\) × full height \(n \times r\)". For stairs without a platform, use \(p = 0\). This formula is for solid stairs poured on the ground. It does not work for stairs with a hollow underneath (such as concrete poured onto steel stair pans). For home stairs, the IRC requires a tread depth of at least 10 in and a riser height of at most 7 3/4 in.

Weight of the concrete

Standard notation (the usual math form)

In words (symbols replaced with words)

\(m\) \(=\) \(V\) \(\times\) \(\rho\)

③ \(m\): weight \(=\) ① \(V\): volume \(\times\) ② \(\rho\): density

The formula in words

① Take the \(V\): volume (ft³)

② multiply it by the \(\rho\): density (lb/ft³)

③ and you get the \(m\): weight (lb)

Quick example

The weight of 27 ft³ (1 yd³) of plain concrete (density 144 lb/ft³) is

weight \(m\) \(=\) volume (27 ft³) \(\times\) density (144 lb/ft³)

\(27 \times 144 = 3888\,\mathrm{lb}\ \ (1.944\ \text{tons})\)

Key idea

Density (unit weight) is the weight of 1 ft³. In the US, 144 lb/ft³ for plain concrete and 150 lb/ft³ for reinforced concrete are common estimates (reinforced concrete is heavier because of the steel). Real concrete varies with the aggregate and the mix, roughly 140 to 150 lb/ft³ for normal-weight concrete. When you compare with other sources, make sure the density values match. One cubic yard of concrete weighs about 27 × 144 ≈ 3,900 lb, nearly 2 tons. To convert pounds to (US short) tons, divide by 2,000.

Number of bags needed

Standard notation (the usual math form)

\(B\) \(=\) \(\lceil\) \(V\) \(\div\) \(y\) \(\rceil\)

In words (symbols replaced with words)

③ \(B\): bags needed \(=\) \(\lceil\) ① \(V\): volume (ft³) \(\div\) ② \(y\): yield per bag (ft³) \(\rceil\)

The formula in words

① Take the \(V\): volume (ft³)

② divide it by the \(y\): yield per bag (0.6 ft³ for an 80 lb bag) and round up (the symbol \(\lceil\ \rceil\) means "round up")

③ and you get the \(B\): bags needed

Quick example

The number of 80 lb bags (0.6 ft³ each) for 27 ft³ of concrete is

\(27 \div 0.6 = 45\)

\(\lceil 45 \rceil = 45\)

Key idea

You can only buy whole bags, so if the division leaves a decimal, always round up (111.1 bags → 112 bags). Bagged concrete mix in the US comes in 80, 60 and 40 lb bags, and the label shows how much concrete one bag makes (the yield): typically 0.60 ft³ for 80 lb, 0.45 ft³ for 60 lb and 0.30 ft³ for 40 lb. For 27 ft³ that is 45 bags of 80 lb, 60 bags of 60 lb or 90 bags of 40 lb. The yield differs a little by brand and product, so check the bag label when you need many bags. Mixing 45 bags by hand is hard work. Past about 1 yd³, it is usually easier to order ready-mix concrete delivered by truck.

The basic method is to find the volume with the formula for the shape, divide cubic feet by 27 to get cubic yards, and multiply by the density (144 lb/ft³ for plain concrete, 150 for reinforced) to get the weight. For bagged mix, divide the volume by the yield per bag (0.6 ft³ for an 80 lb bag) and round up. It is common to allow 5-10% extra for spills and soaking in.

Symbols and terms

Symbols

\(V\)	vee	The volume of concrete, in cubic feet (ft³). Divide by 27 for cubic yards (yd³).
\(l\)	ell	The length - of the slab or wall, or of the stretch of curb and gutter.
\(w\)	double-u	The width - of the slab (the height for a wall), or the side-to-side width of the stairs.
\(h\)	aitch	The vertical dimension. Depending on the shape it is the slab thickness, the hole depth, the tube length or the curb height.
\(q\)	cue	The quantity - how many of the same thing you build.
\(\pi\)	pi	Pi (about 3.14159), used for the area and volume of circles and cylinders.
\(d\), \(d_{1}\), \(d_{2}\)	dee, dee one, dee two	The diameter. \(d_{1}\) is the outer diameter and \(d_{2}\) is the inner diameter (of the hollow). The radius is diameter ÷ 2.
\(b\)	bee	The curb depth (its horizontal thickness).
\(f\)	eff	The thickness of the gutter flag (the flat slab at the foot of the curb).
\(g\)	gee	The gutter width (the width of the gutter flag in front of the curb).
\(t\)	tee	The tread depth of the stairs (the surface you step on).
\(r\)	ar	The riser height of the stairs (the height of one step).
\(n\)	en	The number of steps.
\(p\)	pee	The depth of the platform (the flat landing behind the top step). It is 0 if there is none.
\(\rho\)	rho	The density (weight of 1 ft³, in lb/ft³). 144 for plain concrete and 150 for reinforced concrete are common values in the US.
\(m\)	em	The weight. It is found with \(m = V \times \rho\); divide pounds by 2,000 for (short) tons.
\(B\)	bee	The number of bags needed. It is found with \(B = \lceil V \div y \rceil\).
\(y\)	why	The yield per bag - how much concrete one bag makes: about 0.60 ft³ for 80 lb, 0.45 ft³ for 60 lb and 0.30 ft³ for 40 lb (see the bag label).
\(\lceil x \rceil\)	ceiling of x	The symbol for rounding up to a whole number (the ceiling function). (Example - \(\lceil 111.1 \rceil = 112\), \(\lceil 45 \rceil = 45\))

Terms

ready-mix concrete	Concrete mixed at a plant and delivered still wet by a mixer truck. It is ordered by volume in cubic yards, often in steps of 1/4 or 1/2 yd³, so the volume you calculate on this page is the basis of your order. Small orders often carry a short-load fee.
bagged concrete mix	A bagged product with the cement, sand and gravel already blended. You just add water and mix. US home improvement stores sell 80, 60 and 40 lb bags. The yield (volume) per bag differs by brand, so check the bag label when you need many bags.
plain concrete	Concrete with no steel reinforcement. About 144 lb/ft³ is a common value for estimating its weight.
reinforced concrete	Concrete with steel reinforcing bars (rebar) inside. It is heavier because of the steel; about 150 lb/ft³ is a common value for estimating its weight.
density (unit weight)	The weight per unit of volume. Normal-weight concrete ranges from about 140 to 150 lb/ft³ depending on the aggregate (gravel and sand) and the mix.
slab	A flat, plate-shaped piece of concrete such as a floor, a patio or a driveway. On this page it also covers the base of a footing.
curb and gutter	A concrete structure poured in one piece - the curb that rises at the edge of the road and the gutter at its foot that carries rainwater. The same cross-section runs along its length, so the volume is "cross-sectional area × length".
riser height	The height of one step. The IRC limits it to 7 3/4 in for home stairs.
tread depth	The depth of the surface you step on. The IRC requires at least 10 in for home stairs.
waste	The concrete lost to spills, forms that bulge and soaking into the ground. It is common to order 5-10% more than the exact amount.

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.

Volume of a rectangular prism (Grade 5)	Knowing that the volume of a box is length × width × height
Area of a circle (Grade 7)	Knowing that the area of a circle is radius × radius × pi Knowing how the diameter and the radius are related (radius = diameter ÷ 2)
Converting units of length and volume (Grades 4–6)	Knowing that 1 ft = 12 in and 1 yd = 3 ft, so 1 yd³ = 27 ft³ Having the habit of putting everything in the same unit before calculating (4 in is 1/3 ft)
Unit rates and density (Grades 6–8)	Understanding a unit rate such as "144 lb per ft³" Knowing that weight = volume × density
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 bags is always rounded up
Algebraic expressions (Grades 6–7)	Being able to substitute numbers into an expression such as \(n(n-1) \div 2\) (used in the stairs formula)

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 volume of a slab, wall or square footing

Length (ft)	9
Width (ft)	9
Thickness (in)	4
Quantity	1
Volume (yd³)	=B1B2(B3/12)*B4/27

Table to find the volume of a column, hole or round footing

Diameter (in)	10
Depth (in)	24
Quantity	10
Volume (ft³)	=PI()(B1/2/12)^2(B2/12)*B3

Table to find the volume of a circular slab or tube

Outer diameter (ft)	10
Inner diameter (ft)	6
Height or thickness (in)	4
Quantity	1
Volume (ft³)	=PI()((B1/2)^2-(B2/2)^2)(B3/12)*B4

Table to find the volume of a curb and gutter

Curb depth (in)	6
Curb height (in)	6
Gutter flag thickness (in)	6
Gutter width (in)	12
Length (ft)	30
Volume (ft³)	=(B1(B2+B3)+B4B3)/144*B5

Table to find the volume of concrete stairs

Tread depth (in)	11
Riser height (in)	7
Number of steps	3
Platform depth (in)	36
Stair width (in)	36
Volume (ft³)	=(B1B2B3(B3-1)/2+B4B3B2)B5/1728

Table to find the weight and the number of 80 lb bags

Volume (ft³)	27
Density (lb/ft³)	144
Weight (lb)	=B1*B2
Weight (tons)	=B3/2000
80 lb bags needed (0.6 ft³ each)	=ROUNDUP(B1/0.6,0)

After pasting, the upper rows of column B are your inputs and the last row is calculated automatically. Enter each dimension in the unit shown in its label; the formulas turn inches into feet with "/12" (and in² into ft² with "/144", in³ into ft³ with "/1728").
"PI()" is pi, and "ROUNDUP(value, 0)" rounds up to a whole number (the ⌈ ⌉ in the formulas).
With the example values, the first table gives 1 yd³, the second about 10.91 ft³ (10 post holes), the third about 16.76 ft³, the fourth 30 ft³ and the fifth about 20.56 ft³.
The sixth table gives a weight of 3,888 lb (1.944 tons) and 45 bags of 80 lb. For 60 lb bags, change 0.6 to 0.45; for 40 lb bags, change it to 0.3. 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 volume of a slab, wall or square footing

Length (ft)	9
Width (ft)	9
Thickness (in)	4
Quantity	1
Volume (yd³)	=B1B2(B3/12)*B4/27

Table to find the volume of a column, hole or round footing

Diameter (in)	10
Depth (in)	24
Quantity	10
Volume (ft³)	=PI()(B1/2/12)^2(B2/12)*B3

Table to find the volume of a circular slab or tube

Outer diameter (ft)	10
Inner diameter (ft)	6
Height or thickness (in)	4
Quantity	1
Volume (ft³)	=PI()((B1/2)^2-(B2/2)^2)(B3/12)*B4

Table to find the volume of a curb and gutter

Curb depth (in)	6
Curb height (in)	6
Gutter flag thickness (in)	6
Gutter width (in)	12
Length (ft)	30
Volume (ft³)	=(B1(B2+B3)+B4B3)/144*B5

Table to find the volume of concrete stairs

Tread depth (in)	11
Riser height (in)	7
Number of steps	3
Platform depth (in)	36
Stair width (in)	36
Volume (ft³)	=(B1B2B3(B3-1)/2+B4B3B2)B5/1728

Table to find the weight and the number of 80 lb bags

Volume (ft³)	27
Density (lb/ft³)	144
Weight (lb)	=B1*B2
Weight (tons)	=B3/2000
80 lb bags needed (0.6 ft³ each)	=ROUNDUP(B1/0.6,0)

The same formulas as in Excel (including the PI() and ROUNDUP 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

shape = "slab"          # slab / column / tube / curb / stairs
density_lb_per_ft3 = 144  # concrete density (plain 144, reinforced 150 lb/ft3)

# enter lengths in feet (4 in = 4 / 12 ft)
if shape == "slab":
    length_ft, width_ft, thickness_ft, quantity = 9, 9, 4 / 12, 1
    volume_ft3 = length_ft * width_ft * thickness_ft * quantity
elif shape == "column":
    diameter_ft, depth_ft, quantity = 10 / 12, 2, 1
    volume_ft3 = math.pi * (diameter_ft / 2) ** 2 * depth_ft * quantity
elif shape == "tube":
    outer_ft, inner_ft, height_ft, quantity = 10, 6, 4 / 12, 1
    volume_ft3 = math.pi * ((outer_ft / 2) ** 2 - (inner_ft / 2) ** 2) * height_ft * quantity
elif shape == "curb":
    curb_depth_ft, curb_height_ft, flag_thick_ft = 0.5, 0.5, 0.5
    gutter_width_ft, length_ft, quantity = 1, 30, 1
    section_ft2 = curb_depth_ft * (curb_height_ft + flag_thick_ft) + gutter_width_ft * flag_thick_ft
    volume_ft3 = section_ft2 * length_ft * quantity
else:  # stairs
    run_ft, rise_ft, width_ft, platform_ft, steps = 11 / 12, 7 / 12, 3, 3, 3
    section_ft2 = run_ft * rise_ft * steps * (steps - 1) / 2 + platform_ft * steps * rise_ft
    volume_ft3 = section_ft2 * width_ft

volume_yd3 = volume_ft3 / 27
weight_lb = volume_ft3 * density_lb_per_ft3
weight_tons = weight_lb / 2000
# bags = volume / yield per bag, rounded up (80 lb: 0.6, 60 lb: 0.45, 40 lb: 0.3 ft3)
bags_80 = math.ceil(volume_ft3 / 0.6)
bags_60 = math.ceil(volume_ft3 / 0.45)
bags_40 = math.ceil(volume_ft3 / 0.3)

print(f"Volume: {volume_ft3:.4f} ft3 = {volume_yd3:.4f} yd3")
print(f"Weight: {weight_lb:.1f} lb ({weight_tons:.3f} tons)")
print(f"Bags: {bags_80} x 80 lb, {bags_60} x 60 lb or {bags_40} x 40 lb")

Runs with the standard library only. Change shape at the top to the shape you are building, replace the dimensions (in feet) and the density with your own numbers, and run it. math.ceil() rounds the number of bags up (the ⌈ ⌉ in the formulas).

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

Volume of a slab, wall or square footing

V = l × w × h × q

V = l \times w \times h \times q

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>V</mi>
    <mo>=</mo>
    <mi>l</mi><mo>&#xD7;</mo><mi>w</mi><mo>&#xD7;</mo><mi>h</mi><mo>&#xD7;</mo><mi>q</mi>
  </mrow>
</math>

V = l * w * h * q

l*w*h*q

V := l*w*h*q;

V = l*w*h*q;

V = l × w × h × q

Volume of a column, hole or round footing

V = π × (d/2)² × h × q

V = \pi \left( \frac{d}{2} \right)^{2} \times h \times q

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>V</mi>
    <mo>=</mo>
    <mi>&#x3C0;</mi>
    <msup>
      <mrow><mo>(</mo><mfrac><mi>d</mi><mn>2</mn></mfrac><mo>)</mo></mrow>
      <mn>2</mn>
    </msup>
    <mo>&#xD7;</mo><mi>h</mi><mo>&#xD7;</mo><mi>q</mi>
  </mrow>
</math>

V = pi (d/2)^2 h q

Pi*(d/2)^2*h*q

V := Pi*(d/2)^2*h*q;

V = pi*(d/2)^2*h*q;

V = π × (d/2)^2 × h × q

Volume of a circular slab or tube

V = π × ((d₁/2)² − (d₂/2)²) × h × q

V = \pi \left\{ \left( \frac{d_{1}}{2} \right)^{2} - \left( \frac{d_{2}}{2} \right)^{2} \right\} \times h \times q

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>V</mi>
    <mo>=</mo>
    <mi>&#x3C0;</mi>
    <mrow>
      <mo>(</mo>
      <msup><mrow><mo>(</mo><mfrac><msub><mi>d</mi><mn>1</mn></msub><mn>2</mn></mfrac><mo>)</mo></mrow><mn>2</mn></msup>
      <mo>&#x2212;</mo>
      <msup><mrow><mo>(</mo><mfrac><msub><mi>d</mi><mn>2</mn></msub><mn>2</mn></mfrac><mo>)</mo></mrow><mn>2</mn></msup>
      <mo>)</mo>
    </mrow>
    <mo>&#xD7;</mo><mi>h</mi><mo>&#xD7;</mo><mi>q</mi>
  </mrow>
</math>

V = pi ((d_1/2)^2 - (d_2/2)^2) h q

Pi*((d1/2)^2 - (d2/2)^2)*h*q

V := Pi*((d1/2)^2 - (d2/2)^2)*h*q;

V = pi*((d1/2)^2 - (d2/2)^2)*h*q;

V = π × ((d_1/2)^2 − (d_2/2)^2) × h × q

Volume of a curb and gutter

V = {b × (h + f) + g × f} × l

V = \left\{ b(h + f) + gf \right\} \times l

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>V</mi>
    <mo>=</mo>
    <mrow>
      <mo>{</mo>
      <mi>b</mi>
      <mrow><mo>(</mo><mi>h</mi><mo>+</mo><mi>f</mi><mo>)</mo></mrow>
      <mo>+</mo>
      <mi>g</mi><mi>f</mi>
      <mo>}</mo>
    </mrow>
    <mo>&#xD7;</mo><mi>l</mi>
  </mrow>
</math>

V = (b (h + f) + g f) l

(b*(h + f) + g*f)*l

V := (b*(h + f) + g*f)*l;

V = (b*(h + f) + g*f)*l;

V = (b(h + f) + gf) × l

Volume of concrete stairs

V = (t × r × n(n−1)/2 + p × n × r) × w

V = \left( t \times r \times \frac{n(n-1)}{2} + p \times n \times r \right) \times w

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>V</mi>
    <mo>=</mo>
    <mrow>
      <mo>(</mo>
      <mi>t</mi><mo>&#xD7;</mo><mi>r</mi><mo>&#xD7;</mo>
      <mfrac><mrow><mi>n</mi><mrow><mo>(</mo><mi>n</mi><mo>&#x2212;</mo><mn>1</mn><mo>)</mo></mrow></mrow><mn>2</mn></mfrac>
      <mo>+</mo>
      <mi>p</mi><mo>&#xD7;</mo><mi>n</mi><mo>&#xD7;</mo><mi>r</mi>
      <mo>)</mo>
    </mrow>
    <mo>&#xD7;</mo><mi>w</mi>
  </mrow>
</math>

V = (t r (n(n-1))/2 + p n r) w

(t*r*n*(n - 1)/2 + p*n*r)*w

V := (t*r*n*(n - 1)/2 + p*n*r)*w;

V = (t*r*n*(n - 1)/2 + p*n*r)*w;

V = (t × r × n(n − 1)/2 + p × n × r) × w

Weight of the concrete

m = V × ρ

m = V \rho

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>m</mi>
    <mo>=</mo>
    <mi>V</mi>
    <mo>&#xD7;</mo>
    <mi>&#x3C1;</mi>
  </mrow>
</math>

m = V rho

V*rho

m := V*rho;

m = V*rho;

m = V × ρ

Number of bags needed

B = ⌈V ÷ y⌉

B = \left\lceil \frac{V}{y} \right\rceil

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

B = |~ V / y ~|

Ceiling[v/y]

B := ceil(V/y);

B = ceil(V/y);

B = ⌈V/y⌉

How to have ChatGPT do the calculation

You are a quantity calculation assistant for concrete 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 pouring a concrete slab 20 ft long, 10 ft wide and 4 inches thick. Use a density of 144 lb/ft³ (plain concrete).
Find each of the following:
1. The volume of concrete (ft³ and yd³)
2. The weight (lb and US tons)
3. The number of bags of concrete mix needed, rounded up, for 80 lb bags (yield 0.6 ft³), 60 lb bags (0.45 ft³) and 40 lb bags (0.3 ft³)
4. The volume, weight and bags with 10% extra for waste

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