leaf area is a major characteristic used to evaluate plant growth. this work aimed to determine a mathematical equation to estimate the leaf area of pistia stratiotes in function of the linear measures of the leaf blades. the experiment was carried out at s？o paulo state university,in jaboticabal-sp, brazil. length (l), width (w) and leaf area (la) of one hundred leaves collected from a natural environment were electronically measured. la and l × w data were submitted to linear regression analysis, determining a mathematical equation to estimate the leaf area of the species. anova on linear regression and correlation analysis between the obtained and estimated leaf area values were significant (p<0.01). leaf area of p. stratiotes may be estimated by the equation: la = 0.79499 (lw).