We aimed to propose a reliable and accurate model using non-destructive measurements of leaf length (L) and/or width (W) for estimating leaf area (LA) of three genotypes of purging nut (<em>Jatropha curcas</em> L.), <em>i.e. Astrea</em> and <em>Barranca</em>, both Colombian and a Mexican genotype. For model construction, ~500 healthy leaves were collected from at least 20 healthy plants naturally grown at each locations, and encompassed the full spectrum of measurable leaf sizes. Equations with L and/or W were generated; however, the best fit were made when product between L and W (LW). To validate these models, independent data set of 450 leaves were used. Thus, we developed a single model (<em>Y_i</em> = β₀ * LW^β1) with high precision and accuracy, random dispersion pattern of residuals and unbiased. In spite of this, a single equation, joining all the studied genotypes, was developed [LA = 0.822 * (LW)^0.983; standard errors: β₀ = 0.020, β₁ = 0.004; R²_a = 0.976], which greatly simplifies the process of measuring the leaf area of the genotypes, a fact that should be highlighted.