Latent heat of fusion of water
| Value | 333.43 kJ/kg (333,430 J/kg) |
| Status | Reference value; the source states no uncertainty |
| Source | IAPWS R10-06(2009) for ice and IAPWS-95 for liquid water at the normal melting point, 273.1525 K and 101325 Pa: 333.43 kJ/kg |
| Categories | ThermodynamicMaterial Properties |
| Unit | Value |
|---|---|
| kilojoule per kilogram | 333.43 kJ/kg |
| joule per kilogram | 333,430 J/kg |
| BTU per pound | 143.3491 BTU/lb |
| foot pound-force per pound | 111,549.86 ft·lbf/lb |
| joule per gram | 333.43 J/g |
| watt-hour per kilogram | 92.619444 W·h/kg |
| calorie per gram | 79.691683 cal/g |
| kilocalorie per kilogram | 79.691683 kcal/kg |
| megajoule per kilogram | 0.33343 MJ/kg |
| kilowatt-hour per kilogram | 0.092619444 kW·h/kg |
Learning zone
Melting a kilogram of ice at 0 °C takes 333.43 kJ and produces a kilogram of water at 0 °C: the energy goes entirely into breaking the crystal lattice, not into raising temperature. Put another way, the heat that melts ice would otherwise warm the same mass of water by 80 K, which is why an iced drink holds its temperature so stubbornly and why glaciers lag the seasons.
Joseph Black identified latent heat in Glasgow in the 1760s by the simple observation that ice in a warm room takes hours to melt while staying at 0 °C the whole time: the first clear evidence that heat and temperature are different quantities, and the conceptual groundwork James Watt built the separate condenser on a decade later. In refrigeration the constant sets the ton: 12 000 BTU/h is the rate needed to melt one short ton of ice in 24 hours.
Cite this page
formula.expert. (2026, November 1). Latent heat of fusion of water. https://formula.expert/constants/latent-heat-fusion-water