Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

New Equations for the Sublimation Pressure and Melting Pressure of H2O Ice Ih



Wolfgang Wagner, T Riethmann, Rainer Feistel, Allan H. Harvey


New reference equations, adopted by the International Association for the Properties of Water and Steam (IAPWS), are presented for the sublimation pressure and melting pressure of ice Ih as a function of temperature. These equations are based on input values derived from the phase-equilibrium condition between the IAPWS-95 scientific standard for thermodynamic properties of fluid H2O and the equation of state of H2O ice Ih adopted by IAPWS in 2006, making them thermodynamically consistent with the bulk-phase properties. Compared to the previous IAPWS formulations, which were empirical fits to experimental data, the new equations have significantly less uncertainty. The sublimation-pressure equation covers the temperature range from 50 K to the vapor-liquid-solid triple point at 273.16 K. The ice Ih melting-pressure equation describes the entire melting curve from 273.16 K to the ice Ih-ice III-liquid triple point at 251.165 K. For completeness, we also give the IAPWS melting-pressure equation for ice III, which is slightly adjusted to agree with the ice Ih melting-pressure equation at the corresponding triple point, and the unchanged IAPWS melting-pressure equations for ice V, ice VI, and ice VII.
J. Phys. & Chem. Ref. Data (JPCRD) -


ice Ih, ice III, ice V, ice VI, ice VII, melting-pressure equation, sublimation-pressure equation, water


Wagner, W. , Riethmann, T. , Feistel, R. and Harvey, A. (2011), New Equations for the Sublimation Pressure and Melting Pressure of H2O Ice Ih, J. Phys. & Chem. Ref. Data (JPCRD), National Institute of Standards and Technology, Gaithersburg, MD, [online],, (Accessed May 27, 2024)


If you have any questions about this publication or are having problems accessing it, please contact

Created December 16, 2011, Updated October 12, 2021