How this calculator works
kWh per day = watts ÷ 1000 × hours; multiplied by your rate from the bill. Rates vary a lot by region, so it is an input rather than a guess.
- kWh per day = watts ÷ 1,000 × hours per day.
- Cost per day = kWh per day × your rate per kWh.
- Per month = cost per day × 30. Per year = cost per day × 365.
Worked example
With these inputs: appliance power 1500; hours used per day 2; your electricity rate per kwh $0.17.
The result is per month $15.30, with per day $0.51 and per year $186.15.
Finding the numbers
Wattage is printed on the appliance's label or in the manual. If it only lists amps, multiply amps by volts (120 V in the US) to get watts. Appliances that cycle on and off, like fridges, heaters with thermostats and AC units, draw full power only part of the time, so estimate the hours they actually run.
Your rate is on your electricity bill: the total energy charge divided by the kWh used gives an all-in rate that includes delivery charges. It's more accurate than the headline supply rate.
Estimating the whole bill
To predict your whole electric bill instead of one appliance, use the Utility Bill Estimator. It adds fixed service charges and taxes to your total usage.
Frequently asked questions
How much does it cost to run a 1,500-watt space heater?
At 1.5 kW for 2 hours a day, it uses 3 kWh daily. At $0.17 per kWh, that's about $0.51 a day, $15.30 a month, or $186 a year.
What is a kilowatt-hour?
The energy used by a 1,000-watt device running for one hour. Utilities bill electricity by the kWh.
How do I lower my electricity bill?
Find the appliances with the largest monthly cost (usually heating, cooling, water heating and dryers), then reduce their hours or replace them with more efficient models. Running this calculator for each shows where the money goes.
Does this work outside the US?
Yes. Enter the rate in your currency per kWh. The watts and hours maths is the same everywhere.