Measurements of 80 to 90 leaves of each of four varieties of spring wheat at various stages of development indicate a fairly close statistical relation between area, and length and width, of the leaf blade. This relation was found to be essentially the same for all four varieties, and from a knowledge of length (L) and median width (W½), the area of an individual leaf was given by the Least Squares relation log.A = 0.0094 + 0.934 log.L + 1.071 log.W½, with a standard error of 4.2% of the antilog. Inclusion of a third measurement, width at three-quarters of the distance from base to tip (W¼), led to the relation log.A = − 0.0438 + 0.970 log.L + 0.880 log.W½ + 0.189 log.W¼, giving estimated values having a standard error of 3.7% of the actual area per leaf.This method of estimating leaf areas (i) is rapid in execution and (ii) does not necessitate removing the leaves from experimental plants, which may accordingly be maintained intact for a series of physiological observations.