⚡ Energy Converter

Convert between joules, calories, kilowatt-hours and BTU. Food energy, electricity bills and heating capacity each use different units — 1 food Calorie (kcal) = 4,184 joules.

From

1 J = 0.001 kJ

Precision

1 joules = 0.001 kilojoules

1 × 0.001 = 0.001

1 J equals 0.001 kJ, so multiplying by 0.001 converts the value. The result describes the exact same quantity — only the measuring stick changes.

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All energy units

Unit	Symbol	Definition
Joule	J	The joule (J) is the SI unit of energy — the work done by a one-newton force over one meter. All other energy units are defined in joules.
Kilojoule	kJ	A kilojoule (kJ) is 1,000 joules. Food energy on labels in Australia, NZ and the EU is stated in kilojoules alongside or instead of kilocalories.
Calorie (small)	cal	A small (gram) calorie (cal) is exactly 4.184 joules — the energy to heat 1 gram of water by 1 °C. Note that food "Calories" are actually kilocalories (1,000 small calories).
Kilocalorie	kcal	A kilocalorie (kcal) is 4,184 joules — identical to the food "Calorie" (capital C) on US nutrition labels. A 2,000-Calorie diet is 2,000 kcal or 8,368 kJ.
Watt-hour	Wh	A watt-hour (Wh) is 3,600 joules — one watt sustained for an hour. Phone and laptop battery capacities are commonly given in watt-hours.
Kilowatt-hour	kWh	A kilowatt-hour (kWh) is 3.6 million joules — the unit on your electricity bill. Running a 1,000 W appliance for one hour uses exactly 1 kWh.
British thermal unit	BTU	A British thermal unit (BTU) is about 1,055 joules — the energy to heat one pound of water by 1 °F. Air conditioners and heaters are rated in BTU per hour.
Foot-pound	ft⋅lb	A foot-pound (ft⋅lb) is the energy of one pound-force acting over one foot, about 1.3558 joules. Torque wrench settings and muzzle energies use foot-pounds.