IP (Inch-Pound) Units and the Btu
The tables and diagrams below were calculated using the REFPROP property package. In the IP unit system, REFPROP converts from SI to IP using the definition of the thermochemical Btu. This is based on 1 calorie = 4.184 J (exact). However, the Fifth International Conference on the Properties of Steam (London, July 1956) defined the International Table calorie as 4.1868 J. This leads to the more widely used International Table Btu = 1.05505585262 kJ. The REFPROP values having units containing Btu were converted to the International Table Btu to construct the tables and diagrams shown below. Comparison directly to REFPROP values that have units of Btu will be slightly different.