Density answers a simple question: how much mass is packed into a given volume? Divide one by the other and you have it — ρ = m/V. That single ratio identifies materials (steel is always ~7,850 kg/m³, whatever the shape), lets you turn a volume into a weight, and decides buoyancy: anything less dense than water floats on it, anything denser sinks. Because the formula links three quantities, knowing any two hands you the third instantly.
Reviewed: June 19, 2026 · Author: Naveen P N, Founder — AI Calculator · Verified against: the definition of density, ρ = m/V.
The density equations
The only pitfall is units: kilograms with cubic metres give kg/m³, grams with cubic centimetres give g/cm³, and the two differ by exactly 1,000. The g/cm³ value doubles as specific gravity — the density relative to water — so a reading of 2.7 g/cm³ means "2.7 times as dense as water." Compare any material's density to the surrounding fluid and you immediately know whether it floats or sinks.
Worked example — will it float?
Scenario: A block of mass 2 kg occupying a volume of 2.5 litres (0.0025 m³).
At 800 kg/m³ the block is lighter than water, so it floats with about 80% submerged — its specific gravity. If instead it were aluminium at 2,700 kg/m³, the same 2.5 litres would weigh 6.75 kg and sink. Density lets you swap freely between these: knowing the material's density and the volume, m = ρ×V gives the mass; knowing the mass and density, V = m/ρ gives the volume.
Frequently Asked Questions
ρ = mass / volume. A 2 kg block of 0.0025 m³ is 800 kg/m³. Keep units consistent (kg+m³ → kg/m³).
m = ρ × V and V = m / ρ. Any two of the three give the third.
÷ 1000. 1 g/cm³ = 1000 kg/m³. Water 1.0 g/cm³, aluminium 2.7. g/cm³ = specific gravity.
Floats if density < fluid's. In water (1000 kg/m³): wood/ice float, metals/stone sink. Trapped air changes apparent buoyancy.
kg/m³: pine 500, water 1000, concrete 2400, aluminium 2700, steel 7850, lead 11340, gold 19300, air ~1.2.