Latent heat is the energy absorbed or released by a substance during a phase change (e.g., solid to liquid, or liquid to gas) at constant temperature. Unlike sensible heat, it does not raise the temperature — it breaks or forms intermolecular bonds.

What formula does this calculator use?

The calculator uses Q = mL, where Q is the heat energy in joules, m is the mass in kilograms, and L is the specific latent heat in J/kg. For fusion (melting/freezing) use the latent heat of fusion; for vaporization (boiling/condensation) use the latent heat of vaporization.

What is the difference between heat of fusion and heat of vaporization?

Heat of fusion (L_f) is the energy required to convert a solid to a liquid (or released when a liquid freezes). Heat of vaporization (L_v) is the energy required to convert a liquid to a gas (or released when a gas condenses). Vaporization typically requires much more energy than fusion.

Why does phase change happen at constant temperature?

During a phase change, all supplied energy goes into breaking or forming molecular bonds rather than increasing kinetic energy (temperature). For example, water stays at 0°C while melting even though heat is being added.

How do I use a negative sign for energy?

A positive Q means the substance absorbs energy (endothermic: melting, boiling). A negative Q means it releases energy (exothermic: freezing, condensation). The magnitude is the same; only the direction changes.

What units does this calculator support?

Mass: grams (g) and kilograms (kg). Specific latent heat: J/kg and kJ/kg. Energy output: joules (J), kilojoules (kJ), and kilocalories (kcal).

Latent Heat Calculator

Calculate heat energy for phase changes (melting, boiling, freezing, condensation) using Q = mL with built-in substance data.

Q = mL Calculator

Select a phase transition, enter the mass, choose or enter the latent heat, then click Calculate.

Phase Transition

Melting (solid → liquid) or Freezing (liquid → solid)

Mass (m)

Specific Latent Heat (L) — of fusion

Result Unit

Result

Enter values and click Calculate

Common Latent Heat Values

Click a row to auto-fill the latent heat field. Values switch automatically with the selected phase.

Substance	L_fusion (kJ/kg)	L_vap (kJ/kg)

Summary

The Latent Heat Calculator uses the formula Q = mL to compute the heat energy exchanged during a phase change — melting, freezing, boiling, or condensation. Unlike sensible heat, latent heat occurs at constant temperature. Enter a mass, select or enter the specific latent heat (L) for the substance, choose the phase transition, and the tool returns the energy in joules, kilojoules, or kilocalories with a step-by-step breakdown.

How it works

Select the phase transition type: fusion (melting/freezing) or vaporization (boiling/condensation).
Choose a substance from the reference table or enter a custom latent heat value.
Enter the mass of the substance.
Select your preferred energy unit for the result.
Click Calculate to see the heat energy Q with a step-by-step solution.
Use the reference table to explore latent heat values for common materials.

Use cases

Determine the energy needed to melt ice in refrigeration or HVAC systems.
Calculate the heat released when steam condenses in a heat exchanger.
Solve physics and chemistry homework problems on phase transitions.
Estimate boiler energy requirements for industrial processes.
Understand energy storage in phase-change materials (PCMs).
Compare latent heat values across substances for materials science research.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu