Density Calculator — mass per unit volume (ρ = m/V)

How it works

Density measures how tightly matter is packed — the mass contained in each unit of volume:

ρ = m ÷ V

where ρ (the Greek letter rho) is the density, m is the mass, and V is the volume. Two objects can have the same mass but very different densities: a kilogram of feathers fills far more space than a kilogram of lead, so the lead is much denser.

This calculator is unit-agnostic — it divides the numbers you enter, so the unit of the answer follows your inputs. Kilograms over cubic metres give kg/m³ (the SI unit); grams over cubic centimetres give g/cm³. Keep the mass unit and the volume unit consistent and the density is in mass-unit-per-volume-unit.

Worked example

Water has a density of about 1000 kg/m³: a mass of 1000 filling a volume of 1 gives 1000 ÷ 1 = 1000. The presets use other reference values from the OpenStax density table — brass at 8440 and blood at 1050 — and a block of mass 600 filling 0.75 of volume, which works out to 600 ÷ 0.75 = 800.

Frequently asked questions

What is the formula for density?

Density equals mass divided by volume: ρ = m/V. Rearranged, mass = density × volume and volume = mass ÷ density, so knowing any two of the three gives the third.

What units is density measured in?

The SI unit is kilograms per cubic metre (kg/m³); grams per cubic centimetre (g/cm³) is also common in chemistry, where water is conveniently 1 g/cm³. This calculator uses whatever consistent mass and volume units you enter — it does not convert between them.

What is the density of water?

About 1000 kg/m³ (equivalently 1 g/cm³) at 4 °C, the temperature of its maximum density. That round number is why water is the reference for *specific gravity* — the density of a substance divided by the density of water.

Why do some objects float and others sink?

An object floats in a fluid when its average density is less than the fluid's. Wood (below 1000 kg/m³) floats on water; a solid steel bar (about 7800 kg/m³) sinks. A steel ship floats because its overall density — steel plus the air inside the hull — is less than water's.

Does density change with temperature?

Usually, slightly. Most materials expand when heated, so the same mass occupies a larger volume and the density drops. That is why the water density above is quoted at a specific temperature; for everyday calculations the change is small enough to ignore.

Why does the result disappear when volume is zero?

Density divides mass by volume, and dividing by zero is undefined — a volume of zero holds no space to contain any mass. The calculator shows a blank result until you enter a positive volume.