Latent Heat Calculator - Solve Phase Transition Energy

A latent heat calculator finds the energy absorbed or released when a substance changes phase, such as ice melting into water or water boiling into steam. The hidden energy that drives a phase change at constant temperature is the latent heat, and the calculator applies Q = m·L with the specific latent heat of the chosen substance and phase transition.

• • Melt ice: Find the energy needed to turn a bag of ice into water at 0 °C, the classic freezer-to-cooler workflow.
• • Boil water: Estimate the energy a kettle, boiler, or steam generator must deliver to vaporize a known mass of water.
• • Cool with ice baths: Plan how much ice is needed to remove a target amount of heat from a coolant loop or reaction bath.
• • Compare refrigerants: Compare R134a and R152a latent heats side-by-side when sizing a refrigeration cycle or heat pump.

The calculator handles both fusion (solid ↔ liquid) and vaporization (liquid ↔ gas) transitions, and a Custom option lets you enter a specific latent heat for substances that are not in the preset list.

Results can be reported in J, kJ, cal, kcal, or BTU so the answer matches your textbook, lab notebook, or HVAC specification.

When the latent heat term is combined with a temperature swing, the mixture-equation solver behind Calorimetry Calculator handles the full sensible-heat plus latent-heat budget.

The calculator applies Q = m·L: the latent heat equals the mass times the specific latent heat of that phase transition. Built-in presets carry standard values for water, ammonia, nitrogen, lead, common refrigerants, and other reference substances.

• m: Mass of the substance, normalized internally to kilograms.
• L: Specific latent heat for the chosen phase transition in kJ/kg (water 334 fusion / 2256 vaporization; presets also cover alcohols, ammonia, CO2, helium, hydrogen, lead, nitrogen, oxygen, R134a, R152a, toluene, turpentine).
• Q: Latent heat absorbed (melting, vaporizing, sublimation) or released (freezing, condensing, deposition), reported in the chosen energy unit.

Each preset is paired with a phase direction: fusion and vaporization absorb heat from the surroundings, while freezing and condensation release the same magnitude back. The result panel reports the magnitude, so you can read the energy either way without re-entering negative values.

If the substance you need is not in the preset list, choose Custom and enter the specific latent heat in kJ/kg from a thermophysical data table; the calculator then performs the same Q = m·L calculation with that value.

According to OpenStax College Physics 2e, the heat required to change the phase of a mass m is Q = m·L, where L is the latent heat of the substance for the chosen phase transition.

If you also need the temperature at which the vaporization step happens, Boiling Point Calculator finds the boiling point from pressure or altitude inputs.

Four ideas turn latent heat from a memorized formula into a working mental model. Knowing them helps you predict the answer before plugging numbers in.

If the phase change happens alongside a temperature swing, total energy is the sum of a sensible-heat term (Q = m·c·ΔT) and a latent-heat term (Q = m·L).

For a single-phase fluid being heated or cooled, sensible heat is the right model and latent heat should be left out.

For the sensible-heat term Q = m·c·ΔT that pairs with latent heat in a full phase-change budget, Specific Heat Calculator solves for any single variable in the energy equation.

The form mirrors Q = m·L: pick the substance, type the mass, and the result panel reports the latent heat in your chosen energy unit.

1. 1 Pick the substance and phase transition: Open the Substance and Phase dropdown and choose the preset for your phase change (Water fusion for ice, Water vaporization for steam, etc.). Pick Custom for anything else.
2. 2 Enter the mass and pick a mass unit: Type the mass and pick grams, kilograms, pounds, or ounces; the calculator converts internally to kilograms.
3. 3 Provide a custom latent heat if needed: If you chose Custom, type the specific latent heat in kJ/kg from your reference table. Leave at zero for any preset.
4. 4 Pick an energy unit: Pick J, kJ, cal, kcal, or BTU; the result panel updates to show the unit alongside the value.
5. 5 Read the latent heat result: The primary result is the total energy absorbed or released; the secondary rows show L and the mass in kilograms for verification.

Melting a 1 kg bag of ice in a camp cooler: pick Water (fusion), enter 1 kg, leave Custom at 0, and select kJ. The result reads 334 kJ, the energy the cooler must absorb to clear the bag.

If the heat has to move through a wall, slab, or pipe on its way to the phase change, Heat Transfer Conduction Calculator applies Fourier's law for that part of the system.

The form replaces a textbook formula, a unit-conversion step, and a phase-table lookup with one consistent workflow.

• • Skip the table lookup: Built-in presets for water, ammonia, nitrogen, oxygen, lead, common refrigerants, and several other substances cover most textbook and lab problems.
• • Mix units freely: Grams, kilograms, pounds, and ounces feed into the same formula after internal conversion, and the answer can be in J, kJ, cal, kcal, or BTU.
• • Fusion and vaporization in one tool: The same form handles ice-to-water, water-to-steam, and sublimation presets like carbon dioxide, so no separate tool per phase is needed.
• • See the intermediate values: Mass in kilograms and specific latent heat are both displayed, so the answer is auditable rather than a black box.
• • Custom L for unusual substances: The Custom option accepts any kJ/kg value from a thermophysical table, so exotic refrigerants, alloys, or organic solvents can be handled.

The biggest gain is consistency: every substance and every unit feeds through the same Q = m·L calculation, so the only thing to think about is whether the phase transition matches the preset you selected.

To translate the latent heat result between joules, kilojoules, calories, kilocalories, and BTU outside the calculator, Energy Converter handles the conversion in either direction.

Even with the right formula, several real-world effects shift the answer. Knowing which ones matter keeps the result honest.

• • The calculator handles one phase change per calculation. A workflow that heats ice from −10 °C to 0 °C, melts it, then boils the resulting water requires two calculations (sensible heat and latent heat) added together, not a single Q = m·L.
• • Built-in latent heat values are tabulated at the normal melting or boiling point. Pressure- or temperature-corrected values need the Custom option or a separate thermophysical property lookup.
• • Mixtures, alloys, and azeotropes do not have a single latent heat value. Use the Custom option with a measured or literature value for the specific composition you are working with.

When the calculator's answer differs from a measured value, the gap is almost always explained by one of these factors.

According to Engineering Toolbox - Latent Heat of Melting, the latent heat of fusion of water is 334 kJ/kg near 0 °C, with other substances ranging from about 13.8 kJ/kg (oxygen) to 339 kJ/kg (ammonia).

According to Engineering Toolbox - Water Properties, the latent heat of vaporization of water at the normal boiling point is 2256 kJ/kg, and the value falls as the saturation temperature rises.

When solutes shift the phase-equilibrium temperature and the effective latent heat, Boiling Point Elevation Calculator quantifies the boiling-point shift from molality and the ebullioscopic constant.