What this calculator does
Density is mass divided by volume, and it is what determines whether something floats, how heavy a given quantity of material will be, and whether two substances will mix or separate into layers.
The convenient reference point is water, at almost exactly 1 gram per cubic centimetre. Anything denser than that sinks in water and anything less dense floats, which is why the calculator reports the ratio directly.
The formula
Divide mass by volume. Working in grams and cubic centimetres gives a figure that compares directly against water at 1.0, and multiplying by 1,000 converts it to kilograms per cubic metre.
| Term | Meaning |
|---|---|
| Density (ρ) | Mass per unit volume. The same material has the same density regardless of how much of it there is. |
| Relative density | Density compared with water. Above 1 sinks, below 1 floats. |
| g/cm³ and kg/m³ | Two common units for the same quantity. One gram per cubic centimetre is exactly 1,000 kilograms per cubic metre. |
The inputs explained
| Field | What to enter |
|---|---|
| Mass (g) | The mass of the sample, in grams. |
| Volume (cm³) | The volume the sample occupies, in cubic centimetres. One millilitre is one cubic centimetre. |
When to use it
Identifying a material
Density is a property of the substance rather than of the sample, so measuring it is a quick way to narrow down what something is made of.
Working out the weight of a quantity
Knowing density converts a volume of material into a mass, which is what matters for transport and load limits.
Predicting whether something floats
Comparing against water settles the question immediately, without needing to test it.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What densities do common sample sizes give?
The same volume at a range of masses.
| Mass | Density | In kg/m³ |
|---|---|---|
| 100 g | 0.5000 g/cm³ | 500.0 |
| 200 g | 1.000 g/cm³ | 1,000.0 |
| 500 g | 2.500 g/cm³ | 2,500.0 |
| 1000 g | 5.000 g/cm³ | 5,000.0 |
Questions
Why does the same material always have the same density?
Because density is a ratio. Taking twice as much of a substance gives twice the mass in twice the volume, so the ratio between them does not change. That is what makes it useful for identifying materials.
Does density change with temperature?
Yes, though usually slightly. Most materials expand when heated, which increases volume while mass stays the same, so density falls. Water is unusual in being densest at about 4°C rather than at freezing.
Why is water the reference?
Partly convenience and partly history: the gram was originally defined so that one cubic centimetre of water has a mass of one gram. It makes relative density easy to read straight off the figure.
Does a hollow object still follow this?
The calculation gives the average density of whatever occupies the volume, air included. That is exactly why a steel ship floats: the hull encloses enough air that the average density of the whole vessel is below that of water, even though steel itself is far denser.
For whether something will float and by how much, see the buoyancy calculator. For pressure produced by a column of liquid, see the pressure calculator.