A simple expression for the saturation vapour pressure of water in the range $minus$50 to 140$deg$C

Let p 3 = p s exp(13·3815 t -1·9760 t 2 -0·6445 t 3 -0·1299 t 4 ) where t =(1- T s / T ), T is absolute temperature, suffix s denotes the steam point and p s is standard atmospheric pressure, exactly 101 325 N m −2 . Then p 3 differs from the saturation pressure p of water vapour over a plane surface of the pure liquid phase at temperature T , as predicted by the generally accepted formulations, by less than ±0·1% of p at all temperatures between −50 and 140°C.