Skip to content
Calcapedia
Menu
Earth & Energy

Electricity Cost Calculator

Estimate what an appliance costs to run per day, month and year from its watts (or amps and volts), hours of use and your price per kWh.

Level: Grades 6–7

Printable worksheet

Electricity Cost Calculator

Know the answer you need? Pick an input to work backward.

Inputs
Power rating

Printed on the appliance's label or power adapter.

Enter your rate from your bill.

Result

Cost per month

$29.20

A 1,500 W appliance used 4 h a day, 7 days a week, uses about 182.5 kWh and costs about $29.20 a month at $0.16 per kWh.

Cost per day of use
$0.96
Cost per week
$6.72
Cost per year
$350.40
Energy per day of use
6 kWh
Energy per month
182.5 kWh
Energy per year
2,190 kWh

See the step-by-step solution ↓

Step-by-step solution

  1. Turn watts into kilowatts, the unit your bill uses (1 kW = 1,000 W)

    1,500 W1,000=1.5 kW

  2. Find the energy used each day: kilowatts times hours of use

    1.5 kW×4 h=6 kWh

  3. Find the cost for each day of use: energy times your price per kWh

    6 kWh×$0.16=$0.96

  4. Count the days of use in a year: days per week times 365, divided by the 7 days in a week

    7×3657=365 days

  5. Find the yearly cost: the cost per day times the days of use

    $0.96×365=$350.40

  6. Split the yearly cost over 12 months to get an average month

    $350.4012=$29.20

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

What this calculator does

Find out what it costs to run an appliance each day, month and year. Every electric appliance has a power rating in watts. Your utility charges for energy in kilowatt-hours (kWh), and one kWh is 1,000 watts used for one hour. Put those together with how long the appliance runs, and you have its running cost.

The calculator works for a space heater, a gaming PC, a dehumidifier or anything else. It shows the cost per day of use, per week, per month and per year, along with the energy used.

If the label lists amps and volts instead of watts, switch the power rating option and enter those. The calculator multiplies them to get watts. You always enter the electricity price yourself, from your bill. Rates differ a lot between providers, plans and times of day.

Where it's used

Why this math matters outside the classroom:

  • Space heaters. A 1,500 W space heater run 8 hours a day uses 12 kWh, about $1.80 a day at $0.15 per kWh.
  • Household bills. Families compare a 100 W TV on 5 hours a day, 0.5 kWh, with other appliances to see what drives the bill.
  • Appliance upgrades. Homeowners compare an old fridge with an efficient new one to estimate how long the savings take to cover its price.
  • Amps and volts. Students find a 10 A, 120 V appliance draws 1,200 W, so an hour of use is 1.2 kWh.

Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 6.RP.A.3.b, 6.RP.A.3.d. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Choose whether you know the appliance's watts, or its amps and volts. Enter the number from its label or power adapter.
  2. Enter how many hours a day it runs and how many days a week you use it.
  3. Enter your rate from your bill, in dollars per kWh. If your bill lists delivery charges separately, use the total price per kWh, including them.
  4. Read the monthly cost first. Then see the daily, weekly and yearly cost and the kilowatt-hours.

What the inputs mean

Power
The rated power. Some appliances switch on and off by themselves, such as fridges, heaters with thermostats and air conditioners. Their average draw is lower than the rating. A plug-in energy meter gives a more accurate number.
Voltage
In the US, a standard outlet is about 120 V. Large appliances such as dryers use 240 V.
Hours used per day
The hours the appliance is really drawing power on a day you use it, from 0 to 24.
Days used per week
How many days a week you use it, from 0 to 7. Decimals are fine, such as 3.5 for every other day.
Electricity price
Enter your rate from your bill. That's your total energy charges divided by the kWh used, or the per-kWh price on your plan.

Formula and method

watts = amps × volts   (if amps and volts are given)
kWh per day = watts ÷ 1,000 × hours per day
cost per day = kWh per day × price per kWh
days per year = days per week × 365 ÷ 7
cost per year = cost per day × days per year;  cost per month = cost per year ÷ 12

In the formulas, amps measure electric current and volts measure the push behind it. A kilowatt-hour is the energy a 1,000-watt appliance uses running for one hour. Dividing watts by 1,000 gives kilowatts, and multiplying by hours gives kilowatt-hours. Your price per kWh turns that into money.

A year is counted as 365 days, or 52 1/7 weeks. A month is one twelfth of a year, about 30.4 days. So the monthly number is an average month, not a specific one.

Worked example

A 1,500 W space heater runs 4 hours a day, 7 days a week, and electricity costs $0.16 per kWh.

  1. Power: 1,500 W ÷ 1,000 = 1.5 kW.
  2. Energy per day: 1.5 kW × 4 h = 6 kWh.
  3. Cost per day: 6 kWh × $0.16 = $0.96.
  4. Days per year: 7 × 365 ÷ 7 = 365. Cost per year: $0.96 × 365 = $350.40.
  5. Cost per month: $350.40 ÷ 12 = $29.20, using 182.5 kWh.

Result: The heater costs about $29.20 a month ($350.40 a year, $0.96 a day). It uses 2,190 kWh a year.

Understanding the result

Use the yearly cost to judge whether an upgrade pays for itself. Say a more efficient model saves $60 a year and costs $180 more. Then it pays for itself in about three years.

Power-hungry appliances used in short bursts, like a kettle or a hair dryer, often cost less than you'd think. Modest ones that run all day, like a dehumidifier or an old freezer, can cost more. That's because energy is power multiplied by time.

Assumptions and limitations

  • The appliance draws its full rated power for every hour you enter.
  • The price per kWh is the same at all times of day.
  • With amps and volts, power is amps × volts. That's exact for appliances that just make heat, such as heaters, and close for motors and electronics.
  • It doesn't handle rates that change by time of day or by how much you use (tiers), fixed monthly charges or taxes. If your bill has tiers, enter an average price per kWh.
  • Appliances with a thermostat or variable speed use less than their rating on average.
  • Standby power, used when the appliance is “off” but still plugged in, isn't included unless you add it as hours of use.

Frequently asked questions

Where do I find the wattage?

Look for a label on the back or bottom of the appliance, or on its power adapter. It may show watts (W), or volts and amps, which you can enter instead. For an exact number, a plug-in energy meter measures the real draw over time.

How do I find my price per kWh?

Your bill lists the kWh you used and the charges. Divide the energy and delivery charges by the kWh to get an all-in price per kWh. Some plans list a single per-kWh price. Others have several lines that you can add together.

Why is my real bill different?

The calculator covers one appliance at its rated power. Your bill includes every device in your home, plus fixed service charges and taxes. And many appliances switch on and off rather than drawing full power the whole time.

Does leaving something on standby cost much?

Each device usually draws only a few watts on standby, but it does so 24 hours a day. A 5 W standby load is 0.12 kWh a day. At $0.16 per kWh, that's about $7 a year. Enter the standby watts and 24 hours to check your own devices.

How this calculator is checked

Method: Energy = power × time (kWh = kW × h); cost = energy × unit price; P = V × I for the amps-and-volts option. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

Embed this calculator

Put this Electricity Cost Calculator on your own website or blog for free. Paste this code where you want it to appear: