A unit of heat originally defined as the amount of heat required to raise the temperature of 1 gram of water through 1 C (the gram-calorie or small calorie).
Different variants of calorie that have seen use:
- International Steam Table calorie = 4.1868 joules
- Mean calorie = 4.19002 joules
- Thermochemical calorie = 4.184 joules
- 15 C calorie = 4.18580 joules
- 20 C = 4.1890 joules
Also, the kilocalorie is 1000 times as large as a calorie. It's also known as a large calorie, kilogram calorie, dietary calorie, nutritionist's calorie, nutritional calorie, and in US consumer products is simply called Calorie -- usually but not always with a capital C.
For most scientific measurements, the calorie has been superseded by the joule, which isn't affected by starting temperature and atmospheric pressure.
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use