Enter any two of power, time, or energy to calculate the third, with conversions among kW/W, hours/minutes/seconds/days, and Wh/kWh/J.
kW to Wh Conversion Formula
Wh = kW × 1000 × h
From volts and amps:
Wh = V × A × PF × h
Solving for power or run time:
kW = Wh ÷ (1000 × h) h = Wh ÷ (kW × 1000)
- Wh = energy in watt-hours
- kW = power in kilowatts (1 kW = 1000 W)
- h = run time in hours
- V = voltage in volts
- A = current in amps
- PF = power factor (use 1 for DC or purely resistive AC loads)
The formula assumes power stays constant over the run time. For loads that cycle on and off (refrigerators, HVAC), use the average power draw, not the nameplate rating. 1 Wh = 3600 J.
Reference Values
Typical power draws and the energy they use over one hour:
| Device | Power | Energy in 1 h |
|---|---|---|
| LED bulb | 0.010 kW | 10 Wh |
| Laptop | 0.06 kW | 60 Wh |
| Refrigerator (avg) | 0.15 kW | 150 Wh |
| Microwave | 1.0 kW | 1,000 Wh |
| Space heater | 1.5 kW | 1,500 Wh |
| Electric kettle | 2.0 kW | 2,000 Wh |
| EV Level 2 charger | 7.2 kW | 7,200 Wh |
Quick unit conversions:
| From | To | Multiply by |
|---|---|---|
| kW | W | 1,000 |
| kWh | Wh | 1,000 |
| Wh | J | 3,600 |
| minutes | hours | ÷ 60 |
Example
A 2 kW space heater runs for 3 hours.
- Wh = 2 × 1000 × 3 = 6,000 Wh (or 6 kWh)
A 1500 W microwave runs for 5 minutes.
- Convert time: 5 ÷ 60 = 0.0833 h
- Wh = 1.5 × 1000 × 0.0833 = 125 Wh
FAQ
Is kW the same as kWh? No. kW measures power, the rate of energy use. kWh measures energy, the total amount used over time. A 1 kW load running for 1 hour uses 1 kWh (1,000 Wh).
Why is power factor needed for AC? On AC circuits with motors or inductive loads, voltage and current are not perfectly in phase. Real power (W) equals V × A × PF. For DC and resistive loads (heaters, incandescent bulbs), PF is 1.
How do I find Wh on a battery? Multiply the battery voltage by its amp-hour rating. A 12 V, 100 Ah battery stores 1,200 Wh.
