[′went‚wərth ‚klas·ə·fə′kā·shən] (geology) A logarithmic grade for size classification of sediment particles starting at 1 millimeter and using the ratio of 1/2 in one direction (and 2 in the other), providing diameter limits to the size classes of 1, ½, ¼, etc. and 1, 2, 4, etc.