Latent Heat Calculator
The energy absorbed or released by a phase change — melting, freezing, boiling or condensing — at constant temperature.
The hidden energy in melting and boiling.
How the latent heat calculator works
Q = mL. Latent heat is the energy a phase change absorbs without any temperature rize at all: the heat goes into breaking the bonds holding the phase together.
The magnitudes are startling. Boiling one kilogram of water takes 2.26 MJ — more than five times the energy needed to heat it from freezing to boiling in the first place. That is why steam burns are so much worse than hot-water burns.
Formula: Q = m L
Worked examples
| Inputs | Energy | Note |
|---|---|---|
| Boiling 1 kg of water | 2,260,000 J | 2.26 MJ — 5.4× the energy to heat it 0→100 °C |
| Melting 1 kg of ice | 334,000 J | 334 kJ |
| Melting 1 kg of lead | 24,500 J | only 24.5 kJ |
FAQFrequently asked questions
What is latent heat?
Energy absorbed or released by a phase change with no temperature change — it goes into breaking or forming bonds instead.
Why does boiling take so much more than melting?
Melting only loosens the lattice; boiling separates the molecules completely against atmospheric pressure. For water it is 2,260 kJ/kg against 334.
Why are steam burns worse?
Because condensing steam dumps 2,260 kJ per kilogram into your skin before it has even started to cool.
Why does sweating cool you?
Evaporation draws its latent heat from your skin. A gram of sweat removes about 2.4 kJ.
Why does ice keep a drink at 0 °C?
Because all the incoming heat goes into melting rather than warming. The temperature cannot rize until the last ice is gone.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Institute of Standards and Technology — the US measurement authority
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.