Energy and power units
Power is energy per unit time (W = J/s), while utility bills charge for energy in kWh — a 100 W bulb running 10 hours uses 1 kWh.
Unit converter
Enter a value — results update instantly.
| From | To | Multiply by |
|---|---|---|
| 1 kWh | joules (J) | 3.6e6 |
| 1 kWh | kcal | 860.421 |
| 1 kcal (food Calorie) | kJ | 4.184 |
| 1 BTU | joules (J) | 1055.06 |
| 1 watt (W) | J/s | 1 |
| 1 kilowatt (kW) | watts | 1000 |
| 1 mechanical hp | watts | 745.7 |
| 1 metric ps | watts | 735.5 |
| 100 W bulb × 10 h | kWh | 1 |
Notes
- Food “Calories” on labels are kilocalories (kcal).
- Electrical hp ratings on motors may use slightly different conventions.
Frequently asked questions
- How many joules are in 1 kWh?
- 1 kilowatt-hour equals 3.6 million joules (3.6 × 10⁶ J), since 1 kWh = 1000 W × 3600 s.
- Is a food Calorie the same as a calorie?
- No — the “Calorie” on food labels (with a capital C) is a kilocalorie, equal to 1000 small calories or about 4.184 kJ.
- How many watts is one horsepower?
- One mechanical horsepower is about 745.7 W, while one metric horsepower (PS) is about 735.5 W.