Solve density, mass or volume from the other two, in any units.
Density is mass per unit volume: ρ = m / V. Water has a density of 1 g/cm³ (= 1000 kg/m³) at 4 °C — this is the reference for specific gravity. Materials denser than water (ρ > 1 g/cm³) sink; those lighter float. The calculator converts between common metric and US customary units before and after the calculation.
Density
Density = Mass ÷ Volume
Pure water at 4 °C has a density of exactly 1 g/cm³ (1000 kg/m³). At 25 °C it is slightly less, 0.997 g/cm³. Sea water is denser at about 1.025 g/cm³.
Specific gravity is the ratio of a substance's density to the density of water. Because water is 1 g/cm³, specific gravity and density in g/cm³ are numerically equal. Steel (specific gravity ≈ 7.8) is 7.8× denser than water.
Use the water displacement method: fill a graduated cylinder with a known volume of water, submerge the object, and read the new level. The difference is the object's volume. Then density = mass / displaced volume.
Divide by 1000. 1000 kg/m³ = 1 g/cm³. This is because 1 m³ = 1,000,000 cm³ and 1 kg = 1000 g, so the ratio is 1000.