Energy converter
Convert energy between J, kJ, cal, kcal, Wh and kWh. Example: 500 kcal is 2,092 kJ; 1 kWh is 3,600 kJ or about 860.42 kcal.
What to know
The energy page converts six units: joule, kilojoule, calorie, kilocalorie, watt-hour and kilowatt-hour. Values pass through joules: 1 kJ = 1,000 J, 1 cal = 4.184 J, 1 kcal = 4,184 J, 1 Wh = 3,600 J and 1 kWh = 3,600,000 J.
The calorie used here is the thermochemical calorie of exactly 4.184 J. Food labels that say Calories or kcal are 1,000 of these, so a 500 kcal meal is 500 x 4184 / 1000 = 2,092 kJ, the figure printed next to kcal on European packaging.
On the electricity side, 1 kWh = 3,600 kJ, and expressed in food calories it equals 3,600,000 / 4,184 = 860.42065 kcal. A phone battery of 15 Wh holds 54,000 J. The default pair is J to kJ.
British thermal units, electronvolts and therms are not included. Energy is different from power: a 2 kW heater running for 3 hours uses 6 kWh, which you can compute on the power page and then convert here.
Appliance labels show the contrast between the units: a 100 W bulb used for 10 hours consumes 1 kWh, which is 3,600 kJ or 860.42065 kcal. A banana of around 100 kcal holds 418.4 kJ.
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How to use Energy converter
- Enter 500 as the Value.
- Select kcal in From and kJ in To.
- Read the Result line, which shows 2,092 kJ.
- Set From to kWh and To to kcal, enter 1, and read 860.42065 kcal.
Quick answers
How many kJ is a 2,000 kcal day?
8,368 kJ, from 2000 x 4.184.
Is a food Calorie the same as a calorie?
A food Calorie is a kilocalorie, which is 1,000 of the small calories used in physics. Select kcal for nutrition labels.
How many joules are in a watt-hour?
Exactly 3,600 J, since one watt for one hour is 1 x 3,600 seconds.