Kilojoules to Ergs (kJ to erg)

1 kilojoule equals 10,000,000,000 ergs exactly.

1 kilojoule = 10,000,000,000 ergs

How to convert kilojoules to ergs

To convert kilojoules to ergs, multiply the number of kilojoules by 10,000,000,000. This factor is exact. To go the other way, multiply ergs by 1×10⁻¹⁰.

ergs = kilojoules × 10,000,000,000

Example: 10 kilojoules = 100,000,000,000 ergs.

The 'calorie' on food labels is really a kilocalorie. The thermochemical calorie (4.184 J) is used here unless marked IT.

About these units

Kilojoule (kJ)

Metric (SI)Current unit

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

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.

1 kilojoule = 1,000 joules (exactly).

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

Erg (erg)

CGS & old metricTraditional unit (still used in some regions)

Exactly 10⁻⁷ joules. The energy unit of the old centimeter-gram-second (CGS) system, still used in astrophysics.

Erg takes its name from the Greek ergon, meaning work. Rudolf Clausius proposed that word for a unit of energy in 1864, and in 1873 a British Association committee including Maxwell and Thomson asked that erg be reserved for the energy unit of the centimeter-gram-second system.

It is the work done by a force of one dyne acting through one centimeter, or 1 g cm2/s2. That equals 10 to the power minus 7 joule, 100 nanojoules, which is a very small amount of energy and was a natural size for laboratory experiments of the era.

The erg is not an SI unit, and NIST lists it only as a conversion factor to the joule. It survives mainly in astrophysics and theoretical physics, where Gaussian CGS units remain common, so cosmic energies are still often given in ergs.

1 erg = 1×10⁻⁷ joules (exactly).

Sources: Wikipedia: Erg (unit); Wikipedia: Centimetre-gram-second system of units; NIST SP 811, Appendix B.8 conversion factors

Related conversions

See all energy units.