ABSTRACTEven small colloidal clay fractions in suspension affect markedly the results from a hydrometer test. The discrepancies are due to non‐consideration of specific gravity and relative viscosity of the actual clay‐water suspension. Therefore, actual—i.e., experimentally or otherwise determined—values of specific gravity and relative viscosity should be used instead of the conventionally used values for the specific gravity and the coefficient of viscosity. Expressed in terms of this study, in equations 1 and 2 the values ofG1andnshould be replaced byG11andnr,respectively. Another simple but time‐consuming remedy is to remove the clay content from the soil by repeated decantation before conducting the hydrometer