Calculate density, mass or volume with metric and imperial unit support
Density is the amount of mass per unit volume of a substance: ρ = m/V (density equals mass divided by volume). It's one of the fundamental physical properties used to identify materials, calculate buoyancy, design storage and shipping, and determine whether objects float or sink. Water has a density of approximately 1 g/cm³ (1000 kg/m³) at 4°C — this is not a coincidence but the historical definition of the gram. Ice floats on water because it's less dense (0.917 g/cm³); steel sinks because it's denser (7.87 g/cm³).
This calculator solves for any variable in the density equation: given mass and volume it finds density, given density and volume it finds mass, given density and mass it finds volume. It also provides reference density values for common materials (metals, liquids, gases, woods) and supports unit conversion between g/cm³, kg/m³, lb/ft³, and lb/in³.
The gram was historically defined as the mass of 1 cm³ of water at 4°C — the temperature at which water achieves maximum density. So water = 1 g/cm³ = 1000 kg/m³ = 62.43 lb/ft³ by definition. Water density decreases both above and below 4°C (due to ice crystal structure), which is why ice floats.
Ice has a hexagonal crystal lattice structure that is actually less dense than liquid water. Water expands by about 9% when freezing, so ice (0.917 g/cm³) is less dense than water (1.0 g/cm³). This anomalous property of water is rare in nature and is critical for aquatic life — if ice sank, lakes and oceans would freeze solid from the bottom up.
Specific gravity (relative density) is the ratio of a substance's density to the density of water. Specific gravity of gold = 19.3 (gold is 19.3× denser than water). Specific gravity is dimensionless. For liquids, specific gravity determines whether they float on water: gasoline (SG ≈ 0.71) floats; saltwater (SG ≈ 1.025) sinks pure water. For gases, specific gravity is usually relative to air.
Most materials expand when heated, increasing volume while mass stays constant — so density decreases with temperature. This is used in convection: hot air is less dense and rises; cool air is denser and sinks. Exceptions: water between 0–4°C becomes denser as it warms (until 4°C), and some materials undergo phase changes that change density non-linearly.
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