Heat Units

We will use the symbol Q for heat. Heat is a form of energy, actually energy transfer. The SI unit for energy is the Joule (J), and therefore the official SI unit for heat is also the Joule.

Other commonly used units:

1 calorie (cal) = amount of heat needed to raise the temperature of 1 g of water by 1 ^oC (from 14.5 ^oC to 15.5 ^oC)
1 kilocalorie (kcal) = 1000 cal
The energy value of food is measured in kcal. But in this context, the kcal is usually referred to with an upper case C: Calorie (Cal). => 1 Cal = 1000 cal
1 British thermal unit (Btu) = amount of heat needed to raise the temperature of 1 lb of water by 1 ^oF (from 63 ^oF to 64 ^oF). => 1 Btu = 252 cal = 0.252 Cal
Btu ratings on barbecues or air conditioners are actually Btu/hour (power)
The relationships between the calorie and other non-SI units and the Joule are:

1 cal = 4.1868 J
1 Cal = 1 kcal = 4186.8 J
1 Btu = 1055 J = 0.252 kcal

You can find energy unit conversions in our javaScript engine section.