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Energy Converter
Convert between joules, calories, kilowatt-hours, BTU, electronvolts, and foot-pounds. Used in nutrition, physics, electricity billing, HVAC, and thermodynamics.
Energy is measured in different units depending on the field. Nutrition uses kilocalories (kcal) commonly called "calories". Electricity bills use kilowatt-hours (kWh). Physics uses Joules. HVAC and heating use British Thermal Units (BTU). Understanding these conversions helps compare energy costs and understand nutrition labels.
Calories and Kilocalories
A food "calorie" (Cal or kcal) = 1,000 physics calories (cal) = 4,184 Joules. The calorie on food labels is actually a kilocalorie. A 2,000 kcal daily diet = 8,368,000 Joules = 2.324 kWh of energy.
Kilowatt-Hours and Joules
1 kWh (the unit on your electricity bill) = 3,600,000 Joules (3.6 MJ). A typical home uses 30 kWh/day = 108,000,000 J. An LED bulb (10W) running for 1 hour = 0.01 kWh = 36,000 J.
BTU for Heating and Cooling
BTU (British Thermal Unit) = the energy to raise 1 pound of water by 1°F = 1,055.06 J. Air conditioners are rated in BTU/hour. A 12,000 BTU/hr AC = 1 ton of cooling = 3,516 watts.
Frequently Asked Questions
1 calorie (physics/chemistry) = 4.184 Joules. However, food "calories" are actually kilocalories (kcal): 1 food calorie = 1 kcal = 1,000 cal = 4,184 Joules. A chocolate bar with 200 kcal contains 836,800 Joules of energy.
1 kilowatt-hour (kWh) = 3,600,000 Joules (3.6 MJ). This is the amount of energy used by a 1,000-watt appliance running for 1 hour. Your electricity bill charges per kWh, typically $0.10-0.20 per kWh in the US.
A BTU (British Thermal Unit) is the amount of energy needed to raise 1 pound of water by 1 degree Fahrenheit. 1 BTU = 1,055.06 Joules = 0.000293 kWh. Air conditioner capacity is measured in BTU/hr.
Multiply kWh by 3,412.14 to get BTU. For example: 1 kWh = 3,412 BTU. To convert BTU to kWh, divide by 3,412.14. A 12,000 BTU/hr air conditioner uses about 3.52 kWh per hour.
An electronvolt (eV) is a tiny unit of energy used in particle physics and atomic science. 1 eV = 1.602 × 10⁻¹⁹ Joules. The energy of visible light photons ranges from about 1.8 to 3.1 eV.
1 ton of AC cooling = 12,000 BTU/hr = 3,517 watts = 3.517 kW. The "ton" originally referred to the cooling effect of melting one ton of ice over 24 hours. A typical home needs 2-5 tons of AC capacity.