The average thickness of tabular silver bromide grains can be calculated from the magnitude of the specific dye adsorption if some estimate of the average grain diameter is available. Using 1,1′-diethyl 2,2′-cyanine chloride as the dye, we related the calculated grain thicknesses, in the range from 30 to 150 nm, to data from atomic force microscopy. To bring these two methods into agreement, a limiting molecular area of 0.62 ± 0.01 nm² had to be assigned, which is 10% higher than the reported value for octahedral {111} faces. Dye adsorption gives a result close to the number average thickness of the grains, unless there exists a significant correlation between grain thickness and diameter.