Enter a value in any energy unit and instantly see the equivalent in joules, kWh, calories, BTU, eV and more.
| Unit | Value |
|---|
Energy shows up in wildly different unit systems depending on the field: physicists use joules and electronvolts, electrical engineers and utility bills use kilowatt-hours, chemists and nutrition labels use calories, and US heating bills use therms and BTU. This tool lets you enter a value once and see it converted to every common energy unit at the same time — no need to look up a from/to pair.
Every energy unit converts through the joule (J), the SI base unit of energy. To convert from unit A to unit B:
Unlike power units (which include the non-linear dBm scale), every energy unit is a simple linear multiple of the joule — so all conversions here are straightforward multiplication or division.
| Unit | Symbol | Value in Joules |
|---|---|---|
| Joule | J | 1 |
| Kilojoule | kJ | 1,000 |
| Megajoule | MJ | 1,000,000 |
| Gigajoule | GJ | 1,000,000,000 |
| Watt-hour | Wh | 3,600 |
| Kilowatt-hour | kWh | 3,600,000 |
| Megawatt-hour | MWh | 3,600,000,000 |
| Calorie (thermochemical) | cal | 4.184 |
| Kilocalorie (food Calorie) | kcal | 4,184 |
| British Thermal Unit (IT) | BTU | 1,055.056 |
| Therm (US) | therm | 105,480,400 |
| Foot-pound | ft·lb | 1.355818 |
| Electronvolt | eV | 1.602176634 × 10⁻¹⁹ |
| Erg | erg | 1 × 10⁻⁷ |
| Litre-atmosphere | L·atm | 101.325 |
Note: "calorie" above refers to the thermochemical (small) calorie. Nutrition labels use the kilocalorie, commonly written "Calorie" with a capital C. The therm figure uses the US definition (100,000 BTU at 59°F).
Example 1 — kWh to Joules
A household appliance uses 1 kWh of electricity. In joules: 1 kWh × 3,600,000 J/kWh = 3,600,000 J (3.6 MJ).
Example 2 — BTU to kWh
A gas heater rated at 100,000 BTU: 100,000 × 1,055.056 J = 105,505,600 J, then ÷ 3,600,000 J/kWh ≈ 29.3 kWh.
Example 3 — Calories to Joules
A 250 kcal snack: 250 × 4,184 J = 1,046,000 J (about 1.05 MJ) of food energy.
Example 4 — eV to Joules
A photon with 2 eV of energy: 2 × 1.602176634×10⁻¹⁹ J = 3.204 × 10⁻¹⁹ J — a good illustration of why the eV exists as a practical unit at atomic scales.