Specific heat capacity is the slope (derivative) of the internal energy due to random motion of atoms in a sample as a function of temperature, normalized by dividing by the mass of the sample. Because the internal energy curve is normally almost linear, it can by approximated by measuring the heat required to raise the temperature of 1 kg of a substance by 1 °C (or one Kelvin). The SI unit of measurement for this is the Joule per kilogram-kelvin ( J·kg-1·K-1). 1 J/(kg·K) is identical to 1 m2/(s2·K), which is non-intuitive, but involves only SI base units.
Factors that influence heat capacity measurements: