Although numerical results for evaporation rates from arbitrarily shaped particles have been recently reported in the literature, it remains of interest to explore construction and accuracy of approximate analytical expressions that are simple and of general use. We have analyzed the popular equivalent-volume approximation and also the inscribed sphere approximations in this context, using a technique due to Zhang and Stone (J. Fluid Mech. 367 (1998) 329) who had studied rotatory oscillations of nearly spherical bodies. Comparison of the approximate results with accurate numerical results shows that both these approximations are quite useful. The equivalent-volume sphere approximation is particularly 2 attractive as the error is of the order e, where e is a measure of departure from the spherical shape.