Heating a material takes energy, and the equation for heat transfer tells you how much. This guide covers the sensible heat form, specific heat values, and how the energy form differs from the rate at which heat moves.

The equation for heat transfer

The sensible heat form of the heat transfer formula is:

Q = m × c × ΔT

m is the mass, c is the specific heat, and ΔT is the temperature change. Specific heat is the energy to raise one kilogram by one degree, so water at 4186 J/kg·°C needs far more energy than steel at about 490. The heat transfer calculator applies this and returns joules and kilojoules.

Worked example

Heating 2 kg of water by 10°C: Q = 2 × 4186 × 10 = 83,720 J, about 83.7 kJ. Water dominates many results because its specific heat is high, which is why it works so well as a coolant.

Specific heat of common materials

Values in J/kg·°C: water 4186, air 1005, aluminum 900, steel 490, copper 385. The lower the specific heat, the faster a material changes temperature for the same energy. Heat also makes a solid grow, which the thermal expansion formula measures.

Energy versus rate of heat flow

Q = m c ΔT gives how much energy changes the temperature. How fast that heat moves is a separate calculation and depends on the mode: conduction through solids in contact, convection in a moving fluid, and radiation carried by infrared waves. To turn the energy into a heating time, divide it by the heater power. Heating and cooling equipment is rated in BTU per hour, which the BTU calculator sizes for a room.

Related heat calculations

For a whole room rather than one mass, the heat load calculator adds gains and losses across walls, windows, people, and equipment.

Common mistakes

• Wrong specific heat. Water is far higher than metals, so use the right value.
• Confusing energy with rate. This gives joules, not the watts a heat flow calculation returns.
• Ignoring phase change. Melting or boiling needs extra latent heat beyond Q = m c ΔT.

Quick reference

Heat energy: Q = m × c × ΔT. Water c = 4186 J/kg·°C. Run your own numbers with the free tools on CalculateGuide.