The energy to heat (or cool) a mass through a temperature change, Q = m·c·ΔT — in joules, kJ and kWh — and the power needed if you set a heat-up time.
Q = m · c · ΔT. This is sensible heat only — it does not include the extra energy of a phase change (melting or boiling), which needs the latent heat. Real heaters also lose energy, so add an efficiency margin.