**Heat capacity** or **thermal capacity** is the ability of an object to store heat. It is abbreviated to C_{th}, and its SI units are J/K (joule per kelvin). The concept is further discussed in the article on temperature.

Heat capacity is related to thermal capacitance by the formula

- V = volume (m
^{3}) - ρ = density (kg/m
^{3}) - c
_{p}= specific heat (J/kgK) at constant pressure

_{p}is known as

*thermal capacitance*or (confusingly)

*thermal capacity*, and has units of J/m

^{3}K. Dulong and Petit predicted in 1818 that ρc

_{p}would be constant for all solids (the Dulong-Petit law). In fact, the quantity varies from about 1.2 to 4.5 J/m

^{3}K. For fluids it is in the range 1.3 to 1.9, and for gases it is a constant 0.001 J/m

^{3}K.