[en] Gamma-radiation data obtained on Madras beach has been analysed and it is found that there is a good negative correlation between the grain size and the observed gamma ray activity. A method has been proposed to utilize this correlation to obtain average grain size by much easier procedure, in comparison to sieve analysis, using the gamma-radiation intensity. This procedure can be used where the beach sand is not having anomalously high radiations (which are caused by monazite and other minerals). A case study from marina beach area, Madras is presented and it is suggested that this method can be applied to other areas by developing correlation relationships for the area under investigation. (author). 4 refs., 2 figs