Kilojoule (kJ)

Metric (SI)Current unit

1,000 joules. Food labels in many countries give energy in kilojoules.

1 kilojoule = 1,000 joules (exactly).

About the kilojoule

Most food labels around the world express energy in kilojoules, which is the calorie's long retirement in action. The calorie came out of heat measurement, and the 1948 CGPM resolution stated that the joule should be preferred as the unit of heat. Labels that still show kilocalories alongside kilojoules rely on the thermochemical calorie of exactly 4.184 joules, so one kilocalorie is about 4.184 kJ.

The kilojoule is a convenient size for a body's daily bookkeeping. A person at rest uses about 5,000 kJ, or roughly 1,200 kcal, per day, and the recommended intake for a moderately active woman is given as 2,000 food calories, which is about 8,400 kJ.

Smaller physical comparisons land in the same range. One watt-hour is 3.6 kJ, a British thermal unit is about 1.1 kJ, exploding a gram of TNT releases about 4.2 kJ, and an alkaline AA battery holds about 9 kJ.

Sources: Wikipedia: Kilojoule; Wikipedia: Joule; Wikipedia: Orders of magnitude (energy)

Kilojoule conversion chart

1 kilojoule expressed in every other energy unit:

More Metric (SI) units

• joule (energy)
• megajoule (energy)
• gigajoule (energy)
• millijoule (energy)
• watt-hour (energy)
• kilowatt-hour (energy)
• megawatt-hour (energy)
• tonne of oil equivalent (energy)
• meter (length)
• kilometer (length)
• centimeter (length)
• millimeter (length)
• micrometer (length)
• nanometer (length)
• picometer (length)
• decimeter (length)

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