Density Calculator

Density (ρ, the Greek letter rho) measures how much mass is packed into a given volume, calculated as ρ = m ÷ V, where m is mass and V is volume. It is an intensive property, meaning it doesn't depend on the size of the sample — a teaspoon of gold and a gold bar have the same density, even though their masses and volumes are very different. The SI unit of density is kilograms per cubic meter (kg/m³), though grams per cubic centimeter (g/cm³) and grams per milliliter (numerically identical to g/cm³) are common in chemistry and everyday reference.

Because ρ = m ÷ V, the formula rearranges into two other useful forms: mass = density × volume, and volume = mass ÷ density. As with speed, distance, and time, this can be visualized as a triangle — m on top, ρ and V side by side underneath — covering the quantity you want reveals whether the remaining two should be multiplied or divided. This calculator applies exactly this logic depending on which quantity you choose to solve for.

Specific gravity (also called relative density) is the ratio of a substance's density to the density of a reference substance, usually water at 4°C, which has a density of almost exactly 1,000 kg/m³ (1 g/cm³). Because it's a ratio of two densities, specific gravity has no units — a specific gravity of 2.7, for example, means a substance is 2.7 times as dense as water. Water was chosen as the reference precisely because its density is so close to a clean, round 1,000 kg/m³ at standard conditions.

An object floats in a fluid when its average density is less than the fluid's density, and sinks when it's greater — a direct consequence of Archimedes' principle, which states that a floating or submerged object displaces a volume of fluid whose weight equals the buoyant force pushing back on it. Ice (about 917 kg/m³) floats on water (about 1,000 kg/m³) because it is less dense, despite being the same substance in solid form — one of the relatively rare cases where a solid is less dense than its liquid. A steel ship floats not because steel is less dense than water (it is roughly 8 times denser), but because its hollow hull gives the ship as a whole an average density lower than water.

Densities vary enormously across materials: air at sea level is about 1.2 kg/m³, water is about 1,000 kg/m³, aluminum is about 2,700 kg/m³, steel is about 7,850 kg/m³, gold is about 19,300 kg/m³, and osmium — the densest naturally occurring element — is about 22,590 kg/m³. Density is temperature-dependent, and for gases and liquids, pressure-dependent too: nearly all substances expand and become less dense as they warm, so a density result is only fully meaningful alongside the temperature and pressure at which the input values were actually measured.