Kilowatt Hour Calculator
Convert watts and hours of use per day, up to 24, to kWh, then see what an appliance costs to run per day, month and year at your rate. How it works
Use the Kilowatt Hour Calculator
About the Kilowatt Hour Calculator
kWh = watts × hours ÷ 1,000. A 1,500 W heater running for 2 hours uses 1,500 × 2 ÷ 1,000 = 3 kWh, and a 10 W LED bulb takes 100 hours to use 1 kWh. The kWh calculator takes hours of use per day, up to 24, and repeats that day for the monthly and yearly totals; for a one-off run longer than a day, multiply the daily figure by the number of days.
kWh used at common wattages
| Power | kWh per hour | kWh per month at 1 hour a day | kWh per month at 8 hours a day | kWh per month, always on |
|---|---|---|---|---|
| 5 W (phone charger) | 0.005 | 0.15 | 1.22 | 3.65 |
| 10 W (LED bulb) | 0.01 | 0.30 | 2.44 | 7.31 |
| 60 W (incandescent bulb) | 0.06 | 1.83 | 14.61 | 43.83 |
| 100 W | 0.1 | 3.04 | 24.35 | 73.06 |
| 500 W | 0.5 | 15.22 | 121.76 | 365.28 |
| 1,000 W (1 kW) | 1 | 30.44 | 243.52 | 730.56 |
| 1,500 W (space heater) | 1.5 | 45.66 | 365.28 | 1,095.84 |
| 2,000 W | 2 | 60.88 | 487.04 | 1,461.12 |
| 3,000 W | 3 | 91.32 | 730.56 | 2,191.68 |
| 7,200 W (7.2 kW EV charger) | 7.2 | 219.17 | 1,753.34 | 5,260.03 |
The appliances are examples of round wattages; use the figure on your own rating plate. A month is 30.44 days, the same length the calculator uses.
Frequently asked questions
- How do I convert watts to kWh?
- Multiply watts by hours of use and divide by 1,000. Watts alone cannot be converted, because kWh also depends on time: 100 W for 10 hours and 1,000 W for 1 hour are both 1 kWh.
- How much does it cost to run an appliance?
- Cost = kWh × the price per kWh on your electricity bill. If your bill says $0.20 per kWh, the 3 kWh used by a 1,500 W heater in 2 hours costs $0.60. The rate field starts at $0.12 per kWh and that value is used until you change it, so type the price from your bill. Results are shown in US dollars, but the arithmetic is the same for any currency per kWh.
- How many kWh does a 1,500 W heater use?
- 1.5 kWh for every hour it runs. At 8 hours a day that is 12 kWh a day and 365.28 kWh over a 30.44-day month.
- What is the difference between kW and kWh?
- kW is power, the rate at which energy is used. kWh is energy, the amount used over time. 1 kW running for 1 hour is 1 kWh, which equals 3.6 megajoules.
- How does the calculator get monthly and yearly figures?
- It works out kWh per day, then multiplies by 30.44 for a month and by 365.25 for a year. Those are average lengths, so a 31-day bill comes out slightly higher.
- How do I convert kWh back to watts?
- Divide kWh by the hours and multiply by 1,000. 2.4 kWh used over 24 hours is an average draw of 100 W.
Related Tools
View all toolsAppliance Energy Cost Calculator
Running cost of an appliance, or up to five, from watts, hours a day, days a week and your rate: cost per hour, per day, per average month and per year.
Vampire Power Cost Calculator
Annual, monthly and daily cost of standby power from the number of devices, watts each, hours a day and your rate, with kWh and CO2.
Horsepower to kW Converter
Convert hp to kW and kW to hp for mechanical, metric (PS), electric and boiler horsepower: 100 hp is 74.57 kW mechanical.
Power Converter
Convert mW, W, kW, MW, mechanical, metric (PS) and electric horsepower, BTU/h and refrigeration tons: 1 kW is 1.341 hp, 1 hp is 745.7 W.
Energy Converter
Convert J, kJ, cal, kcal, Wh, kWh, MWh, BTU, therms, ft·lbf, erg and eV either way: 1 kWh = 3.6 MJ = 860.42 kcal = 3412.14 BTU = 0.0341 therm.
Server Rack Power Budget
Add up server and device watts to get the rack load in kW, its heat in BTU per hour, a branch circuit size and the monthly and yearly energy cost.