Density Calculator

Density: ρ = m/V

Density tells you how much mass sits in a given volume: ρ = m/V. The SI unit is kg/m³, though at the bench you'll usually reach for g/cm³ or g/mL, which mean the same thing (1 g/cm³ = 1,000 kg/m³). Distilled water at 4 °C comes out to exactly 1.000 g/cm³, and that was how the gram was first defined. Air sits around 1.2 kg/m³, mercury at 13.6 g/cm³, and gold at 19.3 g/cm³, which explains why a real gold bar feels absurdly heavy for its size. Archimedes' principle says that a submerged body pushes aside a volume of fluid equal to its own volume. That's how you measure the volume of an awkwardly shaped object, and it's also where buoyancy comes from.

Applications

Density gives away a material's identity (a "gold" piece reading 8.5 g/cm³ is almost certainly brass, since real gold sits at 19.3). It drives hydrometry in dairies and distilleries, where you compare relative density against water, along with hydrostatic balances. Airships and balloons rely on it too: helium at 0.17 kg/m³ and natural gas around 0.8 kg/m³ both rise in air. Add to that mineral separation by density and quality control of concrete and soils.

FAQ

Is g/cm³ the same as g/mL? In practice, yes. One cm³ equals one mL, and you'll see both units used in the lab.

Why does ice float on water? Ice (≈ 0.917 g/cm³) is actually less dense than liquid water (1.000 g/cm³). That's unusual, and it happens because of how hydrogen bonding spaces the molecules out when water freezes.

What is relative density? It's the ratio between a substance's density and that of a reference, usually water at 4 °C. Because it's dimensionless, it shows up everywhere in hydrometers used for milk, juices and alcoholic drinks.