Energy converter

Energy is the capacity to do work, and work is energy transferred by a force acting over a distance. The SI unit is the joule (J), equal to one newton-meter. Kilojoules appear on food labels in many countries, while electricity is billed in kilowatt-hours, where 1 kWh is exactly 3.6 MJ.

Convert between 10 energy units. Pick any two units below; results update as you type.

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About energy units

The calorie used here is the thermochemical calorie of exactly 4.184 J, and food labels in the US list kilocalories, written as Calories with a capital C. Heating and cooling equipment in the US is rated in British thermal units (BTU); this converter uses the International Table BTU of about 1,055 J. The tonne of oil equivalent (toe), exactly 41.868 GJ, is used for national energy statistics.

Foot-pounds-force and kilogram-force meters express mechanical work in older or customary engineering contexts. They share dimensions with torque, but for energy the joule is the standard choice.

Tips

One food Calorie (kcal) is 1,000 small calories, exactly 4.184 kJ; nutrition labels outside the US often show kJ alongside kcal.
Do not confuse kWh (energy) with kW (power); a 1 kW heater running for 1 hour uses 1 kWh.
Several BTU definitions exist, differing by a fraction of a percent; check which one a specification uses for precise work.

All energy units

Unit	Symbol	Value in joules
Joules	J	1 J = 1 J
Kilojoules	kJ	1 kJ = 1,000 J
Calories	cal	1 cal = 4.184 J
Kilocalories	kcal	1 kcal = 4,184 J
Kilowatt-Hours	kWh	1 kWh = 3,600,000 J
Kilogram-Force Meters	kgf·m	1 kgf·m = 9.80665 J
Inch-Pounds	in·lbf	1 in·lbf = 0.1129848 J
Foot-Pounds	ft·lbf	1 ft·lbf = 1.355818 J
British Thermal Units	BTU	1 BTU = 1,055.056 J
Tonnes of Oil Equivalent	toe	1 toe = 41,868,000,000 J

Factors: NIST SP 811 · SI Brochure · NIST Handbook 44 — Updated October 17, 2026