Electricity Cost Calculator (Appliance Energy Use and Cost)

Enter the power, duty cycle, hours of use and electricity rate. If you pick an appliance preset, typical values for a US household are filled in.

Appliance preset

Power

Power unit

Hours of use

Usage unit

Duty cycle (%)

Electricity rate ($/kWh)

The calculator uses 1 month = 30.44 days and 1 year = 365.25 days. Preset values are only rough guides; the real power and hours depend on the product and how you use it. If the duty cycle is left blank, it is treated as 100%.

Result

Enter the power and hours of use 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
Formula
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 the power (W or kW), duty cycle, hours of use and your electricity rate, and you get the energy use (kWh) and cost per day, week, month and year on the spot
Pick a common household appliance, such as a central air conditioner, a refrigerator or a hair dryer, and typical power, duty cycle and hours of use are filled in for you
Hours of use can be entered in 8 kinds of units, such as "min/day", "hours/week" and "days/month" (1 month = 30.44 days and 1 year = 365.25 days)
A plain-language explanation of the formulas and copy-and-paste formulas for Excel, Google Sheets and Python are all on this page

The starting rate of $0.17 per kWh is close to the average US residential electricity price (U.S. Energy Information Administration, 2025). Actual rates depend a lot on your state, utility and plan, so for an accurate result, use the rate from your electric bill. A simple way to find it is to divide the total of your bill by the kWh you used.

What is this calculation used for?

See whether a new appliance pays for itself (such as a refrigerator)

A refrigerator runs 24 hours a day, 365 days a year, so a difference in efficiency turns straight into a difference in cost. For example, if you replace an old refrigerator that uses 700 kWh a year with a newer, more efficient model that uses about 400 kWh, the difference is 300 kWh. At $0.17 per kWh, that saves about $51 a year, or about $510 over 10 years (all rough estimates).
When you can compare "the extra price of the new model" with "the money saved on electricity" in numbers, you can decide on a replacement by calculation instead of by feel.

Plan for summer bills by estimating the cost of air conditioning

A 3-ton central air conditioner draws about 3,500 W. Running at a 50% duty cycle for 8 hours a day, it uses 14 kWh a day, which costs about $2.38 a day and about $72 a month at $0.17 per kWh.
An air conditioner cycles on and off once the house reaches the set temperature, so it is not running at full power all the time. This is the idea behind the duty cycle. Knowing what each hour costs helps you save energy without being too hot.

Know what your home office or gaming PC costs to run

A 150 W desktop computer used 8 hours a day costs about $6.21 a month. A 30 W laptop costs only about $1.24 (both at $0.17 per kWh).
If you work from home or play PC games for long hours, this difference helps when you choose a computer or estimate your bill. A high-end gaming PC can draw 300 to 500 W or more under load, so the cost changes a lot with how you use it.

Check the cost of leaving things on

A 30 W air purifier left on 24 hours a day costs about $3.73 a month. A 1,500 W space heater at a 50% duty cycle for 5 hours a day costs about $19.41 a month (both at $0.17 per kWh).
The hours of use of a high-wattage appliance matter far more than a small device left on. With this in numbers, you can put your energy-saving efforts in the right order.

How much does it cost to charge a phone?

A phone battery holds about 0.015 kWh (15 Wh), so even a full charge every day costs less than $1 a year (about $0.93 at $0.17 per kWh, not counting charger losses). The worry that overnight charging adds a lot to your bill turns out to be almost nothing once you calculate it.
To really cut your bill, look at the appliances where "wattage × hours of use" is large: air conditioning, heating, water heating and clothes drying.

Formula

Energy use per day (kWh)

Standard notation (the usual math form)

$E$ $=$ $P$ $\times$ $\dfrac{r}{100}$ $\times$ $t$ $\div$ $1000$

In words (symbols replaced with words)

⑤ $E$: energy use per day (kWh) $=$ ① $P$: power (W) $\times$ ② $r$: duty cycle (%) ÷ 100 $\times$ ③ $t$: hours of use per day $\div$ ④ 1000 (Wh to kWh)

The formula in words

① Take the $P$: power (W)

② multiply it by the $r$: duty cycle (%) divided by 100 to get the power actually used,

③ multiply by the $t$: hours of use per day to get the energy per day in Wh,

④ divide by 1000 to change Wh into kWh (kilowatt-hours),

⑤ and you get the $E$: energy use per day (kWh)

Quick example

The energy a 1,500 W space heater uses in one day, running at a 50% duty cycle for 2 hours a day, is

$E$: energy use per day (kWh) $=$ power (1,500 W) $\times$ duty cycle (50%) ÷ 100 $\times$ hours of use (2 hours) $\div$ 1000

$1500 \times \dfrac{50}{100} \times 2 \div 1000 = 1.5$

Key idea

The duty cycle is the share of time, or of full power, that the appliance actually runs. Appliances that run at full power while they are switched on, such as a hair dryer or an electric kettle, are at 100%. Appliances that turn their output up and down to hold a temperature, such as an air conditioner, a refrigerator or a space heater with a thermostat, spend much of the time below the wattage on the label. The final "÷ 1000" changes the energy from Wh (watt-hours) into kWh (kilowatt-hours). Electricity is billed in kWh, so you divide by 1000 to match the unit on your bill (1000 Wh = 1 kWh).

Cost per day ($)

Standard notation (the usual math form)

$C$ $=$ $E$ $\times$ $u$

In words (symbols replaced with words)

③ $C$: cost per day ($) $=$ ① $E$: energy use per day (kWh) $\times$ ② $u$: electricity rate ($/kWh)

The formula in words

① Take the $E$: energy use per day (kWh)

② multiply it by the $u$: electricity rate ($/kWh)

③ and you get the $C$: cost per day ($)

Quick example

If the energy use per day is 1.5 kWh (the space heater in formula 1) and the rate is $0.17 per kWh, the cost per day is

$C$: cost per day ($) $=$ energy use (1.5 kWh) $\times$ rate ($0.17/kWh)

$1.5 \times 0.17 = 0.255$

Key idea

$0.17 per kWh is close to the average US residential price (U.S. Energy Information Administration, 2025). Actual rates vary widely by state and utility, and some plans charge more at certain times of day. To find your own average rate, divide the total on your electric bill by the kWh used that month. In this example the answer is $0.255, or about 26 cents a day.

Converting to a week, month or year

Standard notation (the usual math form)

$E_{n}$ $=$ $E$ $\times$ $n$

In words (symbols replaced with words)

③ $E_n$: energy use for $n$ days (kWh) $=$ ① $E$: energy use per day (kWh) $\times$ ② $n$: number of days in the period

The formula in words

① Take the $E$: energy use per day (kWh)

② multiply it by the $n$: number of days (1 week = 7, 1 month = 30.44, 1 year = 365.25)

③ and you get the $E_n$: energy use for that period (kWh)

Quick example

If the energy use per day is 1.5 kWh, the energy use for 1 month (30.44 days) is

energy use per month (kWh) $=$ energy use per day (1.5 kWh) $\times$ days in 1 month (30.44)

$1.5 \times 30.44 = 45.66$

Key idea

This calculator uses 1 month = 30.44 days and 1 year = 365.25 days. 365.25 days is the average length of a year once leap years (one every 4 years) are spread out, and 30.44 days is that average year divided by 12 months. Cost works the same way: multiply the cost per day by the number of days to get the cost for the period. In the example, 45.66 kWh × $0.17 ≈ $7.76 a month.

To find an appliance's electricity cost, first get the energy use per day in kWh with "power (W) × duty cycle ÷ 100 × hours of use ÷ 1000", then multiply it by your electricity rate ($/kWh). For a week, a month or a year, multiply the daily value by the number of days (7, 30.44 or 365.25).

Symbols and terms

Symbols

$P$	Power. How much electric power the appliance draws, in W (watts). From the word "power".
$r$	Duty cycle. The share (%) of the rated power that is actually used. From the word "rate".
$t$	Hours of use per day. From the word "time".
$E$	Energy use per day, in kWh (kilowatt-hours). From the word "energy".
$u$	Electricity rate. The price of 1 kWh ($/kWh). From "unit price".
$C$	Electricity cost ($). From the word "cost".
$n$	Number of days in the period. This calculator uses 1 week = 7 days, 1 month = 30.44 days and 1 year = 365.25 days.
$E_n$	Energy use for $n$ days (kWh). The small $n$ at the lower right is a subscript that shows how many days.

Terms

Watt	The unit of power, or how fast electricity is being used. You see it on appliance labels, such as "1500 W". 1000 W is written as 1 kW (kilowatt).
kWh (kilowatt-hour)	The unit of energy, or the total amount of electricity used. Using 1 kW of power for 1 hour uses 1 kWh. Your electric bill is based on kWh.
Power rating (wattage)	The power an appliance uses while it runs. The number on the label or in the catalog is often the maximum (rated) power, and the real average can be lower.
Duty cycle	The share of the rated power that is actually used over time. It is below 100% for appliances that cycle on and off to hold a temperature, such as air conditioners and refrigerators.
Average residential electricity rate	The average price US households pay for 1 kWh, published by the U.S. Energy Information Administration (EIA). It was about $0.17/kWh in 2025. Your own rate depends on your state, utility, plan and usage.
Standby power	Power an appliance uses while it is switched off but still plugged in, for things like a remote-control receiver or a clock display. Also called "phantom load". Enter the standby wattage and 24 hours/day in this calculator to estimate its cost.
Rated power	The power the maker states for the appliance running at full capacity. The wattage on the label or in the catalog is usually this value.

Good to know before you start

Here is what helps you understand the calculations on this page, not just use them.
If you get stuck, going back over the topics in this table is the quickest way forward.

Multiplying and dividing decimals (Grade 5)	You can multiply decimals, such as $1500 \times 0.5 \times 2$ Dividing by 1000 moves the decimal point 3 places to the left ($600 \div 1000 = 0.6$)
Percents (Grade 6)	You can change a percent into a decimal, such as "50% is 0.5 of the whole" You know that whole × percent = part
Converting units (Grades 4 to 7)	You know that the prefix k (kilo) stands for 1000 times, so $1\,\mathrm{kW} = 1000\,\mathrm{W}$ You can change minutes into hours, such as 30 minutes = 0.5 hours
Power and energy (middle school physical science)	You can tell power (W, how fast electricity is used) from energy (Wh or kWh, the total amount used) You know that energy = power × time

How to calculate it in Excel

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

Table for energy use per day

Power (W)	1500
Duty cycle (%)	50
Hours of use per day	2
Energy use per day (kWh)	=B1B2/100B3/1000

Table for cost per day

Energy use per day (kWh)	1.5
Electricity rate ($/kWh)	0.17
Cost per day ($)	=B1*B2

Table for weekly, monthly and yearly energy use and cost

Energy use per day (kWh)	1.5
Electricity rate ($/kWh)	0.17
Energy use per week (kWh)	=B1*7
Cost per week ($)	=B3*B2
Energy use per month, 30.44 days (kWh)	=B1*30.44
Cost per month ($)	=B5*B2
Energy use per year, 365.25 days (kWh)	=B1*365.25
Cost per year ($)	=B7*B2

After you paste it, the upper cells in column B are the inputs and the green formula cells show the results automatically.
The first table is the example of 1,500 W at a 50% duty cycle for 2 hours a day, and B4 shows 1.5 (kWh). The second table multiplies that 1.5 kWh by a rate of $0.17, and B3 shows 0.255 ($).
The third table converts the daily values to a week, a month and a year. The cost per month (B6) is about $7.76 and the cost per year (B8) is about $93.14. Just change the numbers in column B to your own appliance's values.

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 for energy use per day

Power (W)	1500
Duty cycle (%)	50
Hours of use per day	2
Energy use per day (kWh)	=B1B2/100B3/1000

Table for cost per day

Energy use per day (kWh)	1.5
Electricity rate ($/kWh)	0.17
Cost per day ($)	=B1*B2

Table for weekly, monthly and yearly energy use and cost

Energy use per day (kWh)	1.5
Electricity rate ($/kWh)	0.17
Energy use per week (kWh)	=B1*7
Cost per week ($)	=B3*B2
Energy use per month, 30.44 days (kWh)	=B1*30.44
Cost per month ($)	=B5*B2
Energy use per year, 365.25 days (kWh)	=B1*365.25
Cost per year ($)	=B7*B2

The formulas use only multiplication and division, so the same formulas as in Excel work as they are. Copy the whole table, paste it into cell A1, and change the numbers in column B to your own.

How to calculate it in Python

power_watts = 1500          # Power (W)
capacity_percent = 50       # Duty cycle (%)
hours_per_day = 2           # Hours of use per day
price_per_kwh = 0.17        # Electricity rate ($/kWh)

# Energy use per day (kWh) = W x duty cycle / 100 x hours / 1000
kwh_per_day = power_watts * capacity_percent / 100 * hours_per_day / 1000

# Energy use (kWh) and cost ($) for each period. 1 month = 30.44 days, 1 year = 365.25 days
for label, days in [("1 day", 1), ("1 week", 7), ("1 month", 30.44), ("1 year", 365.25)]:
    kwh = kwh_per_day * days
    cost = kwh * price_per_kwh
    print(f"{label}: {kwh:.2f} kWh / ${cost:.2f}")

It runs with the standard library only. Change the first 4 values (power, duty cycle, hours per day and rate) to your own appliance's values and run it.

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

Energy use per day (kWh)

E = P × (r ÷ 100) × t ÷ 1000

E = P \times \frac{r}{100} \times t \div 1000

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mrow>
    <mi>E</mi>
    <mo>=</mo>
    <mi>P</mi>
    <mo>&#xD7;</mo>
    <mfrac><mi>r</mi><mn>100</mn></mfrac>
    <mo>&#xD7;</mo>
    <mi>t</mi>
    <mo>&#xF7;</mo>
    <mn>1000</mn>
  </mrow>
</math>

E = P * (r/100) * t / 1000

energy = power*(capacity/100)*hours/1000

E := P*(r/100)*t/1000;

E = P*(r/100)*t/1000;

E = P×(r/100)×t/1000

Cost per day ($)

C = E × u

C = E \times u

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

C = E * u

cost = energy*price

C := E*u;

C = E*u;

C = E×u

Converting to a week, month or year

Eₙ = E × n

E_n = E \times n

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

E_n = E * n

periodEnergy = energy*days

E_n := E*n;

E_n = E*n;

E_n = E×n

How to have ChatGPT do the calculation

You are an electricity cost assistant. Do the calculation below by actually running Python code, and base your answer only on the numbers from the output (do not calculate in your head or guess).

A 1,500 W space heater runs at a 50% duty cycle for 2 hours a day. The electricity rate is $0.17 per kWh.
Find the energy use per day (kWh) with "power (W) × duty cycle ÷ 100 × hours of use ÷ 1000".
Find each of the following (use 1 month = 30.44 days and 1 year = 365.25 days).
1. Energy use (kWh) and cost ($) per day
2. Energy use (kWh) and cost ($) per week, per month and per year

Show the formulas you used and the numbers from the output.

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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\(P\)	Power. How much electric power the appliance draws, in W (watts). From the word "power".
\(r\)	Duty cycle. The share (%) of the rated power that is actually used. From the word "rate".
\(t\)	Hours of use per day. From the word "time".
\(E\)	Energy use per day, in kWh (kilowatt-hours). From the word "energy".
\(u\)	Electricity rate. The price of 1 kWh ($/kWh). From "unit price".
\(C\)	Electricity cost ($). From the word "cost".
\(n\)	Number of days in the period. This calculator uses 1 week = 7 days, 1 month = 30.44 days and 1 year = 365.25 days.
\(E_n\)	Energy use for \(n\) days (kWh). The small \(n\) at the lower right is a subscript that shows how many days.

Multiplying and dividing decimals (Grade 5)	You can multiply decimals, such as \(1500 \times 0.5 \times 2\) Dividing by 1000 moves the decimal point 3 places to the left (\(600 \div 1000 = 0.6\))
Percents (Grade 6)	You can change a percent into a decimal, such as "50% is 0.5 of the whole" You know that whole × percent = part
Converting units (Grades 4 to 7)	You know that the prefix k (kilo) stands for 1000 times, so \(1\,\mathrm{kW} = 1000\,\mathrm{W}\) You can change minutes into hours, such as 30 minutes = 0.5 hours
Power and energy (middle school physical science)	You can tell power (W, how fast electricity is used) from energy (Wh or kWh, the total amount used) You know that energy = power × time

Electricity Cost Calculator (Appliance Energy Use and Cost)

Table of Contents

What you can do on this page

What is this calculation used for?

Formula

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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