The joule is the SI unit of energy, and other units are defined against it: one thermochemical calorie is 4.184 J, one kilowatt-hour is exactly 3.6 million J, and one BTU is about 1,055 J. The food Calorie on nutrition labels is actually a kilocalorie (1,000 calories, 4.184 kJ), which is why labels in many countries show both kcal and kJ. This converter switches between these units for nutrition, electricity bills and heating calculations. A 2,000 kcal daily diet is about 8,368 kJ or 2.32 kWh, and a 1 kW heater running for one hour uses 1 kWh, about 3,412 BTU.
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