Latent Heat Calculator: Q = m L

The heat needed to change the state of a substance without changing its temperature.

Calculated from standard textbook formulas, with every step shown. The formulas are fixed, so the working does not need checking: what matters is the numbers you type in. Use these calculators only if you are competent to choose the inputs (loads, material strength, dimensions, supports) and check your units and assumptions. For learning and checking your own working: design and sign-off are for a qualified engineer. Drafting Central does not store the numbers you type.

How this calculator works

Choose which quantity you want to find.

Enter the other values in the units shown.

The calculator gives the answer with the formula, the substituted numbers, and the answer in other units.

Formulas used

  • Q = mL
  • m = \frac{Q}{L}
  • L = \frac{Q}{m}

Worked example

With the default numbers in the calculator above:

  1. The formula, arranged to find the heat energy: heat energy = mass x specific latent heat
  2. Put the values in (every value in its SI unit): heat energy = 2 x 334000
  3. The answer: heat energy: 668000 J
  4. The same answer in other units: 668 kJ; 0.185556 kWh; 159656 calories

Change the numbers in the calculator to see the full working, every step, for your own case.

Common questions

What is the formula for latent heat?

Heat equals mass times the specific latent heat. Melting 2 kg of ice needs 668 kJ.

What is the latent heat of vaporisation of water?

About 2257 kJ per kg, which is more than six times the heat to melt ice.

Why does the temperature not rise while ice melts?

The heat goes into breaking the bonds of the solid, not into making the molecules move faster.

Related calculators

Got a question about this? Ask an engineering question and get a plain-language answer with references.

Further reading: Any physics or chemistry text (latent heat).

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