The formula
ρ = m / V
| Symbol | Quantity | Unit |
|---|---|---|
| ρ | Density | kg/m³ |
| m | Mass | kg |
| V | Volume | m³ |
What it means
Density is an intrinsic property, which means it does not depend on how much you have. A gram of gold and a tonne of gold have exactly the same density, which is why it identifies a material where mass alone cannot.
How to work it out by hand
- Measure the mass
- Measure or work out the volume
- Divide the mass by the volume
What is worth knowing
Water's density of 1 g/cm³ is not a coincidence but a definition: the gram was originally defined as the mass of a cubic centimetre of water. That makes water the natural reference for whether things float, and it is why 1000 kg/m³ is the number to compare against. Water's other peculiarity matters more: it is densest at 4 °C, not at freezing, so ice floats and lakes freeze from the top down. Almost every other substance is densest as a solid, and if water behaved the same way, lakes would freeze solid from the bottom and very little would survive a winter in them.