A method of calibrating estimates of significant wave height (Hs) from satellite altimeters against buoy data is proposed, which compares monthly means in 2¿ latitude ¿2¿ longitude bins obtained from the satellite data with mean values obtained from hourly buoy measurements. The method is applied to Geosat data, ERS-1 fast-delivery and off-line products and to TOPEX Ku band data. Results for Geosat data are in good agreement with those from earlier work in which individual altimeter and buoy values were compared, lending support to the proposed method. Based upon these results, linear functions are derived for estimating buoy measurements of Hs from ERS-1 and TOPEX altimeter data. Significant differences are found between the ERS-1 fast delivery and off-line values. Regression, from 60¿S to 60¿N, of corresponding 2¿¿2¿ mean wave heights for individual months from ERS-1 and TOPEX confirm that there are significant differences between the data from these satellites. Comparisons of means from ERS-1 and from TOPEX with those from Geosat for the same calendar month but 5 years apart show wider scatter about the regression line, indicating the between-year variability in individual 2¿¿2¿ bins. ¿ American Geophysical Union 1994