Latent heat is the energy absorbed or released by a substance during a phase change, such as melting, freezing, boiling, or condensing, without any change in temperature. The word latent means hidden, because the energy goes into changing the state of the material rather than raising its temperature. The formula is Q = m times L, where m is mass in kilograms and L is the specific latent heat in joules per kilogram.

What is the latent heat of vaporisation of water?

The specific latent heat of vaporisation of water at 100 degrees Celsius is approximately 2260 kJ/kg (2,260,000 J/kg). This means it takes 2260 kilojoules to convert 1 kilogram of water at boiling point into steam at the same temperature. This value is much larger than the latent heat of fusion (melting), which is about 334 kJ/kg.

Why does latent heat not change temperature?

During a phase change, all the energy supplied goes into breaking or forming the intermolecular bonds that hold the substance in its current state, rather than increasing the average kinetic energy of the molecules. Because temperature is a measure of average kinetic energy, it stays constant until the phase change is complete and all the latent heat has been absorbed or released.

Latent Heat Calculator

When a substance changes phase, it absorbs or releases a large amount of energy without any change in temperature. This energy is called latent heat, and it is what makes boiling water such an effective way to transfer heat in cooking and industrial processes, and why melting ice keeps drinks cold. The formula that governs it is simple: Q equals mass multiplied by the specific latent heat of the substance, where Q is in joules, mass is in kilograms, and the specific latent heat L is in joules per kilogram. The specific latent heat of vaporisation (liquid to gas) is different from the specific latent heat of fusion (solid to liquid), and both vary by substance. Water, for example, has an unusually high latent heat of vaporisation at about 2260 kJ/kg, which is why it is so effective as a coolant and why steam burns are so dangerous. The latent heat of fusion for water is about 334 kJ/kg. This calculator supports vaporisation, condensation, melting, and freezing. You choose the phase change type, enter the mass and the specific latent heat for your substance (common presets are provided to help), and the tool returns the total heat energy in joules and kilojoules. The result tells you how much energy must be supplied to drive the phase change, or how much is released if the process goes in the reverse direction.

Calculate.co.nz is proud to be partnered with Premium Homes, a recognised leader in eco-friendly, sustainable, and energy-efficient homebuilding. With a dedicated team and award-winning experience, they create homes that prioritise health, comfort, and long-term performance. Their founders, Andrew and Kelly, set out to raise the standard of residential construction in New Zealand by combining practical building expertise with a clear commitment to doing things better for homeowners.

Phase change type

Substance preset

Mass m

Specific latent heat L

kJ/kg

2260 kJ

heat energy for phase change

In joules2,260,000 J

Per gram2.260 kJ/g

DirectionAbsorbed

Latent heat values vary with pressure and temperature. Standard values are given at atmospheric pressure and the substance's normal phase-change temperature.

How it works

The formula is Q = m × L, where Q is heat energy in joules, m is mass in kilograms, and L is the specific latent heat in joules per kilogram (entered here in kJ/kg and converted internally). For vaporisation and fusion (melting), energy is absorbed from the surroundings. For condensation and freezing, energy is released. The direction field indicates which applies. Per-gram values are calculated by dividing kJ/kg by 1000.

Worked example

You want to boil away 1 kg of water at 100 °C. The specific latent heat of vaporisation of water is 2260 kJ/kg. Using Q = m × L: Q = 1 × 2260 = 2260 kJ (2,260,000 J). The heat is absorbed (energy must be supplied to turn the water into steam). For comparison, melting 1 kg of ice uses L = 334 kJ/kg, so Q = 334 kJ, which is far less. These match the default values in the calculator above.

Related calculators

Heat Transfer Calculator: find the rate of heat flow through conduction or convection.
Enthalpy Calculator: compute sensible heat and enthalpy changes for reactions.
Thermal Expansion Calculator: calculate how solids and liquids expand with temperature.
Energy Converter: convert joules, calories, BTU, and other energy units.

If you've found a bug, or would like to contact us, or learn more about James Graham and Calculate.co.nz.

Calculate.co.nz is partnered with Interest.co.nz for New Zealand's highest quality calculators and financial analysis.

Calculate.co.nz is the sister site of CalculatorHub.com, the world's largest calculator website by tool count.

All calculators and tools are provided for educational and indicative purposes only and do not constitute financial advice.

Calculate.co.nz is proudly part of the Realtor.co.nz group, New Zealand's leading property transaction literacy platform, helping Kiwis understand the home buying and selling process from start to finish. Whether you're a first home buyer navigating your first property purchase, an investor evaluating your next acquisition, or a homeowner planning to sell, Realtor.co.nz provides clear, independent, and trustworthy guidance on every step of the New Zealand property transaction journey.

Calculate.co.nz is also partnered with Health Based Building and Premium Homes to promote informed choices that lead to better long-term outcomes for Kiwi households.

Calculate.co.nz is hosted in Auckland via SiteHost new Zealand.

All content on this website, including calculators, tools, source code, and design, is protected under the Copyright Act 1994 (New Zealand). No part of this site may be reproduced, copied, distributed, stored, or used in any form without prior written permission from the owner.

About & trust: Why Calculate is NZ's most comprehensive · By the Numbers · How we compare · Editorial standards · How we keep data current · NZ finance glossary · Research & data · Financial literacy NZ · About · Privacy policy · Terms of use

Reviewed and maintained. Last reviewed 2026-07-19 and checked on a twice-monthly cycle against IRD, RBNZ and Stats NZ. How we keep data current.