Energy converter
Convert joules, calories, kilowatt-hours and BTU — with the food Calorie and the physics calorie kept a thousand apart.
Common energy conversions
Every energy unit
| Unit | Symbol | In joules |
|---|---|---|
| Joules | J | 1 |
| Kilojoules | kJ | 1,000 |
| Megajoules | MJ | 1,000,000 |
| Watt-hours | Wh | 3,600 |
| Kilowatt-hours | kWh | 3,600,000 |
| Calories | cal | 4.184 |
| Kilocalories | kcal | 4,184 |
| British thermal units | BTU | 1,055.06 |
| Therms | thm | 105,505,585.26 |
| Foot-pounds | ft·lbf | 1.355818 |
| Electronvolts | eV | 1.6022e-19 |
Questions
Is a food Calorie the same as a calorie?
No — it is a thousand of them. The Calorie on a nutrition label is a kilocalorie, written with a capital C in principle and almost never in practice. A 250 Calorie chocolate bar holds 250,000 physics calories, or about 1,046 kilojoules, which is why European labels quote kJ alongside.
What does a kilowatt-hour actually represent?
One kilowatt drawn for one hour — a 1,000 W heater running for sixty minutes, or a 100 W bulb for ten hours. It is the unit your electricity bill is priced in, and it equals exactly 3.6 million joules.
How much energy is one BTU?
Roughly the heat needed to raise one pound of water by one degree Fahrenheit — about 1,055 joules, or the energy in a single kitchen match. Air conditioners are rated in BTU per hour, where a 12,000 BTU/h unit is one "ton" of cooling and draws around 3.5 kW of heat.
Why is the electronvolt so small?
Because it is sized for single particles: it is the energy one electron picks up crossing a one-volt potential difference. At about 1.6 × 10⁻¹⁹ joules it would be absurd for anything larger, which is precisely why particle physics uses it instead of dragging around twenty leading zeros.