We tested 145 samples of 20 different topical medications for the treatment of glaucoma to determine the average drop size of each preparation. The average drop volumes of different preparations varied between a minimum of 25.1 microliter and a maximum of 56.4 microliter, with an average drop volume of 39.0 microliter. Our findings contradict the common assumption that commercial eyedrops contain a volume of 50 to 75 microliters.