Latent heat of vaporisation of water

L_{\mathrm{v}} = 2,256,400\ \text{J/kg}

Value	2.2564 MJ/kg (2,256,400 J/kg) Use in the calculator →
Status	Reference value; the source states no uncertainty
Source	IAPWS-95 (IAPWS R6-95(2018)), computed with CoolProp: 2256.4 kJ/kg at 100 °C on the saturation line
Categories	Thermodynamic Material Properties

Latent heat of vaporisation of water in every specific latent heat unit

Unit	Value
megajoule per kilogram	2.2564 MJ/kg
joule per kilogram	2,256,400 J/kg
kilojoule per kilogram	2,256.4 kJ/kg
BTU per pound	970.07739 BTU/lb
foot pound-force per pound	754,884.4 ft·lbf/lb
joule per gram	2,256.4 J/g
watt-hour per kilogram	626.77778 W·h/kg
calorie per gram	539.29254 cal/g
kilocalorie per kilogram	539.29254 kcal/kg
kilowatt-hour per kilogram	0.62677778 kW·h/kg

This value moves with temperature

Water at any temperature

0 to 100 °CThe value above is one point on this curve. Liquid water from 0 to 100 °C at 1 atm — density, viscosity, specific heat, thermal conductivity and vapour pressure, all at the same state.

Saturated steam at any temperature

100 to 200 °CThe value above is one point on this curve. Dry saturated steam from 100 to 200 °C — saturation pressure, vapour density and latent heat along the boiling line that low and medium pressure steam heating runs on.

Learning zone

Boiling a kilogram of water at 100 °C costs 2256 kJ: 6.8 times the heat of fusion, and enough to raise the same water from freezing to boiling five and a half times over. That enormous energy density is the reason steam is used to move heat around buildings and process plants: condensing one pound of steam releases about 970 BTU at constant temperature, so a steam coil delivers heat without the flow-rate and ΔT juggling a water loop demands.

The value depends strongly on pressure and temperature. It is 2501 kJ/kg at 0 °C, 2442 at 25 °C, the figure used in psychrometrics and evaporative cooling, 2256 at 100 °C, about 2015 at 10 bar, and it falls to zero at the critical point, 373.95 °C and 22.064 MPa, where liquid and vapour become indistinguishable. Evaporative cooling towers and human sweating both trade on the 25 °C value: evaporating 1 % of a water stream cools the rest by roughly 6 K.

Used by 5 solvers

Air Latent Heat (0.68 Rule)

\dot{Q}_l = \rho_a \dot{V} h_{fg} \, \Delta W

Boiler Horsepower to Steam Rate

S = 34.5 \; \text{BHP}

Cooling Tower Heat Rejection

Q = 500 \, R \, \Delta T

Flash Steam Percentage

\%F = \frac{h_{f1} - h_{f2}}{h_{fg2}} \times 100

Latent Heat

Q = m L

Revised 1 November 2026

Cite this page

formula.expert. (2026, November 1). Latent heat of vaporisation of water. https://formula.expert/constants/latent-heat-vaporization-water