This webpage provides an R script for measuring the size diversity and the size evenness of a size distribution. The R script “SizeDiversity_2018” was programmed by J.J. Egozcue and O. Martínez-Abella following the method presented in Quintana et al. (2008) Limnology and Oceanography: Methods, 6:75-86 and updated by Quintana et al. (2016) Limnology and Oceanography: Methods, 14:408-413. It is based on a non-parametric kernel estimation, after data standardization by division of sample geometric mean. This method is applicable to any type of size distribution, even if it doesn’t fit a parametric function, and allows its immediate comparison with the size diversity of other distributions independently of the method used for size estimation. See the above reference for more details on the method. Download the “SizeDiversity_2018” R script and follow the instructions included in the tutorial.