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Latent Heat Calculator

Calculate the heat needed for a phase change at constant temperature.

About Latent Heat Calculator

A phase change absorbs energy without any temperature rise. Water’s latent heat of vaporisation is about 2,260 kJ/kg — enough to raise the same water by more than 500 degrees if it were sensible heat instead. Latent heat is why boiling a pan dry takes far longer than bringing it to the boil, and why evaporative cooling is so effective.

Formula

Latent Heat

Q = m L, where L is the specific latent heat

L
Energy per kilogram absorbed or released during the phase change
constant temperature
Latent heat is exchanged without any temperature change

Worked example

With the default values below, Latent Heat Calculator returns Heat Required for the Phase Change of 668,000.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Massminimum 0 kg
2 kg
Specific latent heatminimum 0.01 J/kg
334,000 J/kg
Available powerminimum 0.01 W
2,000 W
Specific heat capacity for comparisonminimum 0.01 J/kg K
4,186 J/kg K

Results

Heat Required for the Phase Change
668,000.00 J
Heat Required
668.000 kJ
Time at That Power
5.567 min
Temperature Rise the Same Heat Would Cause
79.79 K
Heat Required
0.18556 kWh

Step by step

  1. 1Values used
  2. 2Latent Heat
  3. 3Heat Required for the Phase Change= 668,000.00 J
  4. 4Heat Required= 668.000 kJ
  5. 5Time at That Power= 5.567 min
  6. 6Temperature Rise the Same Heat Would Cause= 79.79 K
  7. 7Heat Required= 0.18556 kWh

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Latent Heat calculated?

Q = m L, where L is the specific latent heat A phase change absorbs energy without any temperature rise. Water’s latent heat of vaporisation is about 2,260 kJ/kg — enough to raise the same water by more than 500 degrees if it were sensible heat instead.

Why does Latent Heat matter?

Latent heat is why boiling a pan dry takes far longer than bringing it to the boil, and why evaporative cooling is so effective.

What values do I need to enter?

This calculator takes 4 inputs: Mass, Specific latent heat, Available power, Specific heat capacity for comparison. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

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