Density Formula
d = m ÷ V: density is mass per unit volume — a characteristic property often used to identify unknown substances.
What it means
Density packs mass and volume into a single number: how much matter sits in each unit of space. Because it is intensive — independent of how much sample you have — it identifies materials: gold's 19.3 g/mL is unmistakable, and water's 1.00 g/mL is the reference everything else is judged against. In the lab it also converts freely between mass and volume whenever one is easier to measure than the other.
Variables
| Symbol | Name | Unit | Meaning |
|---|---|---|---|
| Density | g/mL (or kg/m³) | Mass divided by volume: the intensive property that characterizes the material. | |
| Mass | g | The amount of matter in the sample, measured on a balance. | |
| Volume | mL (or cm³) | The space the sample occupies, measured directly or by displacement. |
Assumptions
- The sample is homogeneous — the same substance throughout.
- Mass and volume refer to the same sample at the same conditions.
- For liquids, note the temperature, since density shifts with it.
- The object is fully measured: mass on a balance, volume by displacement or geometry.
Worked example
A liquid sample with a mass of 42.5 g occupies a volume of 50.0 mL. Calculate its density.
Given:
- Mass of sample = 42.5 g
- Volume of sample = 50.0 mL
Write d = m / V.
Substitute: d = 42.5 g / 50.0 mL.
Divide: 42.5 / 50.0 = 0.850.
Attach units: d = 0.850 g/mL.
At 0.850 g/mL the sample is less dense than water (1.00 g/mL), so it would float on water — consistent with an oil-like liquid.