Subtidal marine sediments from the Belgian continental shelf were measured using laser diffractometry and dry-sieving techniques. The laser diffractometry approach provided a coarser and less-sorted particle size distribution, compared with the dry-sieving technique. The 5th, 10th, 16th, 50th, 84th, 90th, and 95th percentiles, 180–710 μm cumulative mass/volume percentages, mean grain size, and sorting measured using both techniques were correlated, with r2 > 0.76 (p < 0.001). Skewness and kurtosis were poorly correlated between both techniques. For the purpose of conversion of data from one type of measurement to the other, for sandy sediments a global approximation can be obtained with the proposed relationships.