kWh Calculator
Work out how many kilowatt-hours a device uses, or the average power behind a kWh figure, and what that energy costs.
How to use the kWh Calculator
- Choose watts → kWh or kWh → watts.
- Enter the power or energy and the number of hours.
- Optionally enter your electricity rate to see the cost.
How it works
A kilowatt-hour is the energy used by a 1,000-watt load running for one hour. kWh = watts × hours ÷ 1,000, and in reverse watts = kWh × 1,000 ÷ hours. A 100 W bulb left on for 10 hours uses 1 kWh. Your electricity bill charges per kWh, so cost = kWh × rate.
kWh used per hour
| Device power | kWh per hour | kWh per 8 h | Cost per 8 h at $0.17 |
|---|---|---|---|
| 100 W | 0.1 | 0.8 | $0.14 |
| 500 W | 0.5 | 4 | $0.68 |
| 1,000 W | 1 | 8 | $1.36 |
| 1,500 W | 1.5 | 12 | $2.04 |
| 2,000 W | 2 | 16 | $2.72 |
| 3,500 W | 3.5 | 28 | $4.76 |
Frequently asked questions
How many watts is 1 kWh?
kWh is energy, not power: 1 kWh equals 1,000 W for 1 hour, or 500 W for 2 hours.
How many kWh does a house use per day?
A typical US home uses about 25–30 kWh per day, but it varies widely.
How do I find kWh from amps?
Multiply amps × volts to get watts, then watts × hours ÷ 1,000.
What is the difference between kW and kWh?
kW is the rate of power use; kWh is the total energy used over time.