calorie per gram-Celsius
Specific heat capacityexact by definition
The calorie per gram per Celsius degree is the historical metric unit, built on the old definition of the calorie as the heat needed to warm one gram of water by one degree. This catalog uses the thermochemical calorie of exactly 4.184 joules, so one cal/(g·°C) is exactly 4184 J/(kg·K). The factor is exact by definition of the thermochemical calorie, though which calorie is meant is not always stated in older sources.
Watch out: At least four calories are in circulation. The thermochemical calorie is exactly 4.184 J, the International Table calorie exactly 4.1868 J, and the 15-degree calorie about 4.1855 J. They differ by about one part in a thousand, which matters in careful work. Separately, the food Calorie with a capital C is a kilocalorie, a thousand of these.
| 1 cal/(g·°C) | 4,184 J/(kg·K) |
The unit is circular by design: it was defined so that water would have a specific heat of exactly 1. That is still very nearly true, and it is why so many rules of thumb in chemistry treat water's heat capacity as unity.