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Energy Converter

Convert between joules, calories, kWh, BTU and more - all units shown at once.

UnitValue

cal = thermochemical calorie (4.184 J). kcal = food calorie = 1,000 cal.

Use Cases

When to Convert Energy

Nutrition & Diet

Convert food energy between kcal (food calories), kJ shown on nutrition labels, and cal.

Electricity Bills

Understand your kWh consumption by converting it to joules, BTU or megajoules.

Physics & Engineering

Convert between SI energy units (joules) and practical units (kWh, BTU, cal) for problems.

HVAC & Heating

Convert BTU ratings for air conditioners, heaters and boilers to kWh or kJ equivalents.

Solar Energy

Convert solar panel output and daily yield between Wh, kWh and MJ for reporting.

Fuel Calorific Value

Compare the energy content of different fuels listed in kJ/kg, BTU/lb or kcal/kg.

FAQ

Energy Conversion Questions

1 thermochemical calorie (cal) = 4.184 joules. 1 kilocalorie (kcal = food calorie) = 4,184 joules. Nutrition labels in the EU show energy in both kcal and kJ.

1 kWh = 1,000 W × 3,600 s = 3,600,000 J = 3,600 kJ = 3.6 MJ. This is the energy used by a 1,000-watt appliance running for 1 hour.

1 BTU (British Thermal Unit) = 1,055.06 J. It is the energy needed to heat 1 pound of water by 1°F. BTUs are still used widely in the US for air conditioning (e.g. "12,000 BTU AC") and heating systems.

The scientific calorie (cal) = 4.184 J. The food calorie (Cal or kcal) = 1,000 cal = 4,184 J. When a product says "200 Calories," it means 200 kcal. Nutrition labels increasingly show kJ alongside kcal.

1 kWh = 3,600 kJ ÷ 4.184 kJ/kcal = 860.4 kcal. A resting adult needs about 2,000–2,500 kcal/day - roughly equivalent to 2.3–2.9 kWh of electricity (just as an interesting comparison).