Convert an energy quantity
- Enter a nonnegative energy amount and choose its source definition, or choose constant power and duration.
- Select the target unit, checking calorie and BTU variants.
- Convert and review the joule equivalent and multiplier before copying or downloading.
Electrical, thermal and work examples
One kilowatt-hour is 3.6 MJ (3,600,000 J). One watt-hour is 3600 J. A thermochemical calorie is 4.184 J, while an International Table calorie is 4.1868 J. Each kilocalorie is 1000 of its named calories. The selected BTU is the International Table definition, 1055.05585262 J.
Calculation is energy × source joule factor ÷ target joule factor. Definitions follow NIST’s energy table, with the full IT BTU factor also listed in Unicode’s unit definitions. Foot pound-force energy uses international foot and pound-force definitions.
| Unit | Joules per unit |
|---|---|
| Joules (J) | 1 |
| Kilojoules (kJ) | 1000 |
| Megajoules (MJ) | 1000000 |
| Watt-hours (Wh) | 3600 |
| Kilowatt-hours (kWh) | 3600000 |
| Calories (thermochemical) | 4.184 |
| Kilocalories (thermochemical) | 4184 |
| Calories (International Table) | 4.1868 |
| Kilocalories (International Table) | 4186.8 |
| British thermal units (IT) | 1055.05585262 |
| Foot pound-force (energy) | 1.3558179483314006 |
Limits and privacy
Nonnegative source energy quantities up to 10¹⁵; tiny arithmetic underflow rejected. Choose the actual calorie definition instead of relying on “calorie” alone. Other BTU/calorie variants, electronvolts, torque, therms, energy costs and fuel heating values are not supported. Power × time assumes continuous operation at the entered power. It does not estimate appliance cycling, rated-versus-actual consumption or efficiency. Structured input accepts watts, kilowatts or megawatts and seconds, minutes or hours, with each value at most 10¹⁵ and combined energy at most 10¹⁵ J.
Display uses up to 12 significant digits and six decimal places or scientific notation; CSV retains finite floating-point numeric results. Inputs stay in browser memory without requests, uploads or saved amounts. Live conversion updates after a 300 ms pause, with immediate stale-output cleanup. Compare and export all eleven supported units. Power/time CSV preserves both original quantities and their units alongside total joules. Swap keeps the number while reversing units; result reuse preserves the raw quantity and returns structured entry to direct energy mode. These actions, examples and Reset support one Undo step; edits discard that history. Reset clears output and restores one kWh to MJ.
Are kW and kWh interchangeable?
kW measures power, or energy per time. kWh measures energy. Relating them requires a duration; for example, a constant 1 kW for one hour supplies 1 kWh.