About the Latent Heat Calculator
When a substance melts or boils it takes in heat without getting hotter. That heat is the latent heat. This calculator multiplies the mass by the latent heat of the change you choose, such as melting ice or boiling water, and shows the energy in kilojoules, kilowatt-hours and kilocalories. Type the mass and the type of change and the latent heat appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Latent Heat Calculator
- 1Enter the mass and the type of change.
- 2Pick the units or options from the menus if the latent heat tool offers them.
- 3Read the latent heat in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the latent heat
Students use it in physics, and cooks, engineers and HVAC designers use it to see how much energy a phase change takes.
Vaporising takes far more energy than melting, which is why steam burns are severe and why evaporation cools you effectively.
How the latent heat is worked out
Q = mass × latent heat. Melting ice needs 334 kJ per kilogram and boiling water 2,260 kJ per kilogram. Melting 2 kg of ice takes 668 kJ, or 0.186 kWh. Boiling 2 kg of water at 100 °C takes 4,520 kJ, about 1.26 kWh.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Common materials built in
- kJ, kWh and kcal
- Custom latent heat
Mistakes to avoid with latent heat
This tool covers only the phase change itself. Heating the water before it boils needs extra energy from the specific heat, which is not included here.
On phone and computer
On a phone, type into the boxes one after another and read the latent heat underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the latent heat move. The latent heat calculator works the same on both.
Checking your latent heat by hand
A good habit is to test the latent heat calculator with a case you already know. Melting 2 kg of ice takes 668 kJ, or 0.186 kWh. Boiling 2 kg of water at 100 °C takes 4,520 kJ, about 1.26 kWh.
If your own figures give a surprising answer, repeat the working yourself: Q = mass × latent heat. Melting ice needs 334 kJ per kilogram and boiling water 2,260 kJ per kilogram. Small differences usually come from rounding, from mixing units, or from a typing slip in one of the inputs. Melting and boiling need energy without a temperature change, and other heat tools cover the rest. Use the Heat Conduction Calculator for steady flow, the Specific Heat Calculator for warming a material, and the Temperature Converter to switch scales.
Features
- Heating up is separate
- Boiling needs much more than melting
- Use kilograms
- Clear messages when the latent heat inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate latent heat?
Q = mass × latent heat. Melting ice needs 334 kJ per kilogram and boiling water 2,260 kJ per kilogram. Melting 2 kg of ice takes 668 kJ, or 0.186 kWh. Boiling 2 kg of water at 100 °C takes 4,520 kJ, about 1.26 kWh.
What is the formula for latent heat?
Q = mass × latent heat. Melting ice needs 334 kJ per kilogram and boiling water 2,260 kJ per kilogram. The latent heat calculator applies it exactly and rounds only the displayed answer to six significant figures.
Why does the temperature stay constant?
The heat goes into breaking bonds, not speeding up molecules.
What is the latent heat of ice?
About 334 kJ per kilogram.
Does this include heating before the change?
No. That uses specific heat.
Is this latent heat calculator free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.