Heat Energy Calculator
Calculate how much heat energy is needed to change the temperature of a substance, based on mass, specific heat capacity and temperature change.
How to use the heat energy calculator
- Enter the mass of the substance you want to heat or cool, in kilograms.
- Enter the specific heat capacity of the substance — the default value 4186 J/(kg·°C) applies to water.
- Enter the temperature change in degrees Celsius, and the calculator works out the heat energy automatically.
The formula for heat energy
Worked example: heating 1 kg of water by 50 degrees takes 1 × 4186 × 50 = 209,300 J, or just over 209 kJ. With a 2000 W kettle that takes 209,300 ÷ 2000 ≈ 105 seconds, assuming all the power goes into the water.
The heat energy (Q) needed to change the temperature of a substance equals the mass (m) multiplied by the specific heat capacity (c) and the temperature change (ΔT). Heat energy is measured in joules (J).
Specific heat capacity is a material property that tells you how much energy is needed to raise the temperature of 1 kg of the substance by 1 °C. Some common values: water ≈ 4186 J/(kg·°C), ice ≈ 2100 J/(kg·°C), air ≈ 1005 J/(kg·°C), iron ≈ 450 J/(kg·°C). Swap the default value in the calculator for the correct figure for the material you're working with.
Frequently asked questions
What is specific heat capacity?
Specific heat capacity is how much energy is needed to raise the temperature of 1 kg of a substance by 1 °C. It varies from substance to substance and is measured in joules per kilogram per degree Celsius (J/(kg·°C)).
Why does water have such a high heat capacity compared to metals?
Water molecules form strong hydrogen bonds that take a lot of energy to break or set in motion, giving water an unusually high heat capacity. Metals, on the other hand, have simpler atomic structures that heat up faster with less energy, giving them lower heat capacity.
How do I use this to calculate how much energy it takes to heat water?
Enter the mass of the water in kilograms, leave the heat capacity at the default value of 4186 J/(kg·°C), and enter how many degrees you want to raise the temperature. The calculator then shows how many joules (and kilojoules) are needed.