This contribution tests the various measures of grain size used in the paleopiezometry and proposes the frequency peak of the apparent 2D grain size distribution as the most robust estimator. The novelty of the approach resides in the use of the Gaussian kernel density estimator as an alternative to the classical histograms, which improves reproducibility. A free and easy-to-handle script (http://bit.ly/grainSizeTools) was developed with the aim of facilitating the adoption of this measure.