Heat Energy Calculator (Q = mcΔT)
Calculate the heat energy needed to change a substance’s temperature from its mass, specific heat and temperature change.
How it works
Q = m · c · ΔT
The heat needed to warm or cool a substance is its mass times its specific heat times the temperature change. Specific heat measures how much energy each kilogram needs per degree — water’s is unusually high, which is why it heats slowly and stores heat well. A positive result is energy added to warm it; a negative result is energy that must be removed to cool it. This ignores any phase change like melting or boiling.
Worked example
Heating 1 kg of water by 80 K (from 20 °C to 100 °C) needs Q = 1 × 4186 × 80 = 334,880 J ≈ 334.9 kJ, about 80 kcal or 93 Wh.
Sources: Specific heat capacity — Wikipedia
Frequently asked questions
Do I use Kelvin or Celsius for ΔT?
Either works, because a temperature change of one kelvin equals a change of one degree Celsius. Only the difference matters here, not the starting temperature.
Does this include melting or boiling?
No. Q = mcΔT covers heating within a single phase only. Changing state (ice to water, water to steam) needs extra latent heat, which this formula does not add.
Why does water take so much energy to heat?
Its specific heat, about 4186 J/kg·K, is among the highest of common substances. That is why coastal climates are mild and why water is such an effective coolant and heat store.
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Educational estimate. Check the formula and units for your exact case.