Density Converter

Density is mass per unit volume. The SI unit is kg/m³, but g/cm³ is dominant in chemistry and materials work because numerical values land conveniently between 0.5 and 20 for most solids and liquids. lb/ft³ persists in US construction.

Water at 4°C is the reference: 1000 kg/m³, 1.000 g/cm³, 62.43 lb/ft³. Conversions are exact; no temperature correction is applied.

The density of water at 4°C — its temperature of maximum density at standard atmospheric pressure — was the original definition of the kilogram before the 2019 SI redefinition. That historical link is why 1 g/cm³ for water comes out cleanly to 1.000 rather than some inconvenient decimal. The conversion factors among units are exact: 1 g/cm³ = 1000 kg/m³ = 62.42796 lb/ft³ = 8.34540 lb/US-gallon. Material density tables typically quote at 20°C and 1 atm; deviations from those conditions produce small but real shifts that this converter does not apply.

A worked example: aluminum has a quoted density of 2.70 g/cm³ at room temperature. Converting: 2700 kg/m³, 168.55 lb/ft³, 22.53 lb/US-gallon. A solid aluminum cube measuring 10 cm on a side has volume 1000 cm³ and mass 2.70 kg. Compare to lead at 11.34 g/cm³ (708 lb/ft³) — the same cube in lead would weigh 11.34 kg. Density differences this large are why heavy metals feel surprising in the hand.

Limitations: the converter handles unit math only, not temperature or pressure correction. Liquid densities shift by roughly 0.02% per degree Celsius; gas densities shift by about 0.4% per degree Celsius and follow the ideal gas law more strongly. For high-precision work (analytical chemistry, fuel measurement), look up the substance's density at your specific conditions rather than converting from a textbook value. Bulk density (granular materials with air pockets) is a different quantity from material density and depends on packing — sand at 1.6 g/cm³ bulk versus 2.65 g/cm³ true. The converter accepts whatever number you supply; the interpretation is on you.