The “instant” shape of raindrop size distributions (measured during 1 min or less) usually differs from the exponential, generally in the direction of monodispersity. Experimental results are presented for both widespread and thunderstorm rain. It is shown that the measured shape depends significantly on the sample size, and that adding many “instant” distributions from different conditions leads to an exponential distribution such as proposed by Marshall and Palmer. This transition is examined, as well as the sample size needed for a well-defined shape.