The formal stereological transformation equation for particle sieve size distribution from measurements in lower dimensional spaces is applied to laser diffiractometer measurements. The transformation function for iron ore particles is measured experimentally, and modeled. The solution is tested against the measured transformation function data as well as synthetic composite distributions of the original sample. The natural size distribution of a sample taken from a grinding circuit stream was measured by a combination of standard sieving and cyclosizer, and the result is compared to the transformed size distribution calculated from laser diffiractometer measurements. The stereological transformation technique performed well in all cases. (c) 2006 Published by Elsevier B.V.