Sampling errors are highly underestimated in particle size analysis of more or less free-flowing powders. This is wrong. For, such errors often dominate in the results. They consist of two components. The first component is the fundamental error, related to the discrete nature of particulate materials. It determines the minimum amount of sample that has to be taken into account to reach a required precision. This fundamental error can be estimated from the number of particles. The second component is the segregation error. It relates to the segregation that occurs in the batch of material to be sampled or during the sampling process. This segregation error can only be estimated from the analysis results of multiple samples. Guidance on the estimation of both types of sampling errors in relation to the minimum mass and minimum number of primary samples taken from a product lot will be given in this paper.`