Common energy conversions
| From | To | Multiply by |
|---|---|---|
| kcal | kJ | 4.184 |
| kJ | kcal | 0.239006 |
| kWh | MJ | 3.6 |
| BTU | kJ | 1.05506 |
| Calories | Joules | 4.184 |
Food calories
The “Calories” on food labels are kilocalories. A snack with 200 kcal contains 200 × 4.184 ≈ 837 kJ, and many labels print both numbers. A small calorie (cal) is a thousand times smaller, so make sure you pick kilocalorie when converting food energy.
Electricity units
Your electricity bill counts energy in kilowatt-hours, often just called “units”. One unit (1 kWh) is the energy a 1,000-watt appliance uses in one hour, or 3.6 million joules. A 100 W fan running for 10 hours uses 1 unit.
Energy and power
Energy is an amount (joules, kWh); power is how fast energy is used (watts). To convert watts, horsepower or AC tons, use the power converter.