Find the heat energy needed to change a substance's temperature with Q = m c ΔT — or solve for mass, specific heat capacity or temperature change.
Specific heat capacity c is the energy needed to raise 1 kg of a substance by 1 kelvin. The heat to change a mass m by ΔT is Q = m c ΔT, with Q in joules.
Water has an unusually high specific heat (4186 J/kg·K), which is why oceans moderate climate and why it is an effective coolant. A temperature change in kelvin equals the same change in °C, so ΔT can be entered in either.
The heat energy is Q = m c ΔT — mass times specific heat capacity times temperature change. Rearranged, c = Q / (m ΔT).
About 4186 J/(kg·K) (or 4.186 J/g·°C, or 1 cal/g·°C) for liquid water — one of the highest of common substances.
Either works, because a temperature difference is numerically identical in kelvin and Celsius. Only use absolute kelvin when a formula needs the temperature itself, not a change.
Joules per kilogram per kelvin, J/(kg·K), equivalent to J/(kg·°C).