Converters
Energy Converter
Last updated: June 19, 2026
An energy converter is a scientific measurement utility that translates work, heat, and energy values between different unit systems. The converter supports conversions across joules, kilojoules, calories, kilocalories (food calories), watt-hours, kilowatt-hours, British thermal units (BTU), foot-pounds, and electronvolts. It applies standard physical conversion factors to ensure accuracy. Physics students, engineers, nutritionists, HVAC technicians, and electricians use this tool to standardize energy, heat transfer, and electricity consumption measurements across different fields.
Pick a 'from' unit, a 'to' unit, and enter a value. The calculator returns the converted result plus equivalents in every supported energy unit.
Quick Answer
Convert energy, work, and heat values between scientific and consumer units. Enter the value and select units to calculate conversions across joules, calories, BTUs, and kilowatt-hours.
Energy is non-negative. · e.g. 100
Two calorie units differ by 1,000x. 1 small calorie (cal) = 4.184 J. 1 food Calorie / kilocalorie (kcal) = 1,000 cal = 4,184 J. Nutrition labels show kcal (often written as "Calories").
Kilocalorie → Kilojoule
418.4 kj
100 kcal = 418.4 kj
1 cal = 4.184 J (thermochemical). 1 kcal = 1,000 cal = 4,184 J = food Calorie. 1 Wh = 3,600 J. 1 kWh = 3.6 MJ. 1 BTU (IT) ≈ 1,055.06 J.
Examples
100 kcal to kJ
= 418.4 kJ
1 kWh to kJ
= 3,600 kJ
1 BTU to kJ
≈ 1.055 kJ
How it works
All units are stored as factors relative to the joule (the SI base unit of energy). Convert through joules: value times source factor gives joules, then divide by target factor.
Formula · output = value × factor(from) ÷ factor(to)
1 cal = 4.184 J · 1 kcal = 4,184 J · 1 Wh = 3,600 J · 1 kWh = 3.6 MJ · 1 BTU (IT) ≈ 1,055.06 J.
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Frequently asked questions
A small calorie (cal) is the energy to raise 1 gram of water by 1 °C, equal to 4.184 joules. A kilocalorie (kcal) is 1,000 small calories ≈ 4,184 J. Food labels use kcal but commonly write 'Calories' (capital C). A 500-Calorie meal is 500 kcal, not 500 cal. The 1,000x difference matters.
The joule (J) is the SI unit of energy. 1 joule is the energy to apply 1 newton of force over 1 meter, or to pass 1 amp through 1 ohm for 1 second. It's a small unit: 1 food Calorie is over 4,000 J. Most everyday quantities are easier in kJ or kcal.
1 kWh is the energy used by a 1,000-watt appliance running for 1 hour, equal to 3.6 megajoules. It's the standard unit on residential electric bills. Running a 100 W lightbulb for 10 hours uses 1 kWh.
British Thermal Unit. 1 BTU is the energy to raise 1 pound of water by 1 °F, about 1,055 joules. Used in HVAC sizing (a 12,000 BTU/h air conditioner) and heating. 1 BTU/h is a unit of power, not energy.
Yes, in unit-conversion math. Energy is energy regardless of label. They are interchangeable in calculations as long as you respect the conversion factors. The difference is convention: chemists use kJ/mol, nutritionists use kcal, electric utilities use kWh, HVAC engineers use BTU.
Both. The calculator does pure unit conversion; it does not give nutrition advice or thermodynamics interpretation. If you see 'Calories' on a food label, that's kcal. If you see 'kcal/mol' in a chemistry context, that's the same kcal × Avogadro's number.
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