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Energy Converter

Convert energy between joules, calories, kilocalories, kilowatt-hours, BTU, electron volts and more. Free, browser-based, no signup.

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Energy Units

The SI unit of energy is the Joule (J). Different fields use different units: kilowatt-hours (kWh) for electricity bills, kilocalories (kcal) for food energy, BTU for heating and cooling systems, and electron volts (eV) in physics.

Conversion Reference

UnitJoules (J)Common Use
1 calorie (cal)4.184 JChemistry, heat
1 kcal (Food Cal)4,184 JNutrition labels
1 Wh3,600 JSmall battery capacity
1 kWh3,600,000 JElectricity billing
1 BTU1,055.06 JHVAC, heating
1 ft·lb1.35582 JUS mechanical energy

Real-World Energy Examples

A 60W light bulb running for 1 hour uses 0.06 kWh = 216,000 J. A slice of bread contains about 80 kcal = 334,880 J. A AAA battery stores roughly 1.8–3.6 Wh = 6,480–12,960 J.

'How do I convert kWh to joules?', 'a' => '1 kWh = 3,600,000 J (3.6 MJ). Multiply kWh by 3,600,000. For example, 2.5 kWh = 9,000,000 J = 9 MJ.'], ['q' => 'What is a BTU?', 'a' => 'A British Thermal Unit is the energy needed to raise 1 pound of water by 1°F = 1,055.06 J. It is widely used in the US for heating, cooling and gas appliances. Air conditioner capacity is rated in BTU/hour.'], ]" />