Densities of 35 diamonds have been determined by an improved high‐precision flotation method. The density varies from &rgr;25= 3.51477−3.51554 g/cm3. The average density of 35 samples is &rgr;25= 3.51532 g/cm3. The type I diamonds have higher density and narrower range than type II. Comparison with density computed from the lattice constant shows that type II diamonds contain either vacancies (voids) or impurities of lower atomic weight than carbon, or both, and that type I are contaminated by impurities of higher atomic weight than carbon. Computed nitrogen impurity concentration is in excellent agreement with that found by Kaiser and Bond.