An equation for calculating leaf water potential (Ψ1) of cotton (Gossypium hirsutum L.) plants, based on environmental and plant factors, was developed. Two irrigation experiments were conducted with cotton (cv. Acala SJ-2), on a loamy clay soil. Data from 18 treatments of one experiment were pooled and used for multiple regression analysis with Ψ1 as the dependent variable. The parameter displaying the highest correlation with Ψ1 was the reciprocal of the relative soil water content in the upper 105 cm of the soil profile. A regression equation combining this factor with air temperature, an index indicating the crop's water stress history and plant height explained 87% of the variation in Ψ1. The Ψ1 calculated by using this equation showed good correspondence (r = 0.9) with data from eight distinct irrigation treatments of the other experiment. It was shown that Ψ1 of cotton plants can be reliably calculated based on some readily available variables.