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Calculator Answers

Energy Converter

Blake Boege
Written by Blake Boege · Founder, Calculator Answers

An energy converter is a scientific measurement utility that translates work, heat, and energy values between different unit systems. This one supports seven units: joules, kilojoules, calories, kilocalories (the food Calorie), watt-hours, kilowatt-hours, and the IT British thermal unit. Every pair is converted through the joule, and the two factors that are not powers of ten are stated rather than approximated: the thermochemical calorie is exactly 4.184 J and the IT BTU is exactly 1055.05585262 J. 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.

See also: Torque Converter, Power Converter, and Temperature Converter.

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").

Energy

Kilocalorie → Kilojoule

418.4 kj

100 kcal = 418.4 kj

Joule (J)418,400 j
Kilojoule (kJ)418.4 kj
Calorie (small cal)100,000 cal
Kilocalorie (kcal / food Calorie)100 kcal
Watt-hour (Wh)116.222222 wh
Kilowatt-hour (kWh)0.11622222 kwh
BTU (IT)396.566683 btu

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.

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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.