kWh calculator
Turn watts and hours into kilowatt-hours, or work backwards from energy to average power or running time, and price the result.
kWh calculator
Watts or kilowatts. 1 kW = 1,000 W.
Decimals are fine: 30 minutes = 0.5, 15 minutes = 0.25. Up to 8,760 (one year).
Result
Fill in the two fields to see the result.
What is a kilowatt-hour?
A kilowatt-hour (kWh) is the unit electricity is billed in. It is the energy used by something drawing 1,000 watts for one hour. A watt (W) measures power, the rate of use at a moment; a watt-hour (Wh) or kilowatt-hour measures energy, the amount used over time.
The three formulas
- Energy: kWh = watts × hours ÷ 1,000. Example: 100 W for 10 hours = 1 kWh.
- Average power: watts = kWh × 1,000 ÷ hours. Example: 3 kWh over 6 hours = 500 W on average.
- Time: hours = kWh × 1,000 ÷ watts. Example: 1 kWh at 250 W lasts 4 hours.
Minutes need converting to hours first: divide by 60. For example, 2,000 W for 30 minutes is 2,000 × 0.5 ÷ 1,000 = 1 kWh.
From energy to cost
Multiply the energy by your price per kWh. At an illustrative price of $0.20 per kWh, 1 kWh costs $0.20. The calculator also shows the cost per hour at the power entered, which is useful for comparing appliances.
Estimating a whole appliance
To see what an appliance costs per day, week, month and year, use the appliance cost calculator, which also lets you compare several appliances. The methodology explains the time conventions.
Related tools
- Appliance cost calculatorAny appliance, four ways to describe its energy use.
- Refrigerator electricity costUse the yearly kWh figure from the energy label.
- Washing machine electricity costEnergy per cycle multiplied by your loads per week.
- Air conditioner running costRated electrical input, hours of use and a season estimate.
- Standby power costWhat devices cost while plugged in but not in use.