ConverterHub

Energy Converter

Convert between energy units.

How it is calculated

The value is first converted to joules, then to each output unit. Factors used: 1 kJ = 1,000 J; 1 cal = 4.184 J; 1 kcal = 4,184 J; 1 Wh = 3,600 J; 1 kWh = 3,600,000 J. So J = value × factor(from), kJ = J / 1,000, kcal = J / 4,184 and kWh = J / 3,600,000. Results are shown with two decimals, so very small quantities in kWh can appear as 0.00. Here a kcal is the food-label Calorie (1,000 small calories), and the tool uses the thermochemical calorie definition of 4.184 J.

Worked example

Convert 500 kcal. Joules = 500 × 4,184 = 2,092,000.00 J. Kilojoules = 2,092,000 / 1,000 = 2,092.00 kJ. Kilocalories = 2,092,000 / 4,184 = 500.00 kcal. Kilowatt-hours = 2,092,000 / 3,600,000 = 0.58 kWh, which is roughly the energy a 100 W bulb uses in under six hours.

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Common mistakes

  • Confusing a calorie (cal, 4.184 J) with a food Calorie (kcal, 4,184 J); the difference is a factor of 1,000.
  • Mixing up watts (power) with watt-hours (energy); a 1,000 W heater running for one hour uses 1 kWh.
  • Treating kJ and kcal as nearly equal; one kcal is about 4.2 kJ.
  • Expecting a precise tiny value in kWh; two decimals hide very small amounts.

About this calculator

This converter moves energy values between joules, kilojoules, kilocalories (food calories) and kilowatt-hours, the units that show up in physics, nutrition and electricity billing respectively. A food label's "calories" are actually kilocalories, and 1 kWh — what your electricity meter counts — equals exactly 3.6 million joules.

It's used by students solving physics problems that mix units, by anyone comparing a food's energy content to a workout's calorie burn, and by people converting an appliance's rated energy use into the kWh figure that appears on a power bill.

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