About this calculator
Density is how much mass is packed into a given volume. Fill in any two of mass, volume and density and this calculator finds the third, converting between units as it goes.
It also compares the result with water, so you can see whether something would float or sink.
Worked examples
Real numbers, worked out by the same calculator. Press “Use these numbers” to try one above.
500 g in 250 cm³: what density?
- Density
- 2 g/cm³
- Compared with water
- Denser than water: it would sink (2× water's density)
500 g in 250 cm³ has a density of 2 g/cm³.
Show the working
- Density = mass ÷ volume.
- In kilograms and cubic metres: 0.5 kg ÷ 0.00025 m³ = 2,000 kg/m³.
- Show it in g/cm³: 2.
- For comparison, fresh water is about 1 g/cm³ (1,000 kg/m³). Denser things sink in water and less dense things float.
100 cm³ of ice (0.9 g/cm³): what mass?
- Mass
- 90 g
- Compared with water
- Less dense than water: it would float (0.9× water's density)
A volume of 100 cm³ at 0.9 g/cm³ has a mass of 90 g.
Show the working
- Mass = density × volume.
- In kg/m³ and m³: 900 × 0.0001 = 0.09 kg.
- Show it in g: 90.
- For comparison, fresh water is about 1 g/cm³ (1,000 kg/m³). Denser things sink in water and less dense things float.
5.4 kg of aluminium (2,700 kg/m³): what volume?
- Volume
- 2 litres
- Compared with water
- Denser than water: it would sink (2.7× water's density)
5.4 kg at 2,700 kg/m³ takes up 2 litres.
Show the working
- Volume = mass ÷ density.
- In kilograms and kg/m³: 5.4 ÷ 2,700 = 0.002 m³.
- Show it in litres: 2.
- For comparison, fresh water is about 1 g/cm³ (1,000 kg/m³). Denser things sink in water and less dense things float.
1 kg in 2 litres
- Density
- 0.5 g/cm³
- Compared with water
- Less dense than water: it would float (0.5× water's density)
1 kg in 2 litres has a density of 0.5 g/cm³.
Show the working
- Density = mass ÷ volume.
- In kilograms and cubic metres: 1 kg ÷ 0.002 m³ = 500 kg/m³.
- Show it in g/cm³: 0.5.
- For comparison, fresh water is about 1 g/cm³ (1,000 kg/m³). Denser things sink in water and less dense things float.
The formulas
Density = mass ÷ volume, so mass = density × volume and volume = mass ÷ density. 500 g in 250 cm³ has a density of 500 ÷ 250 = 2 g/cm³.
Density is usually written in grams per cubic centimetre (g/cm³) for small things or kilograms per cubic metre (kg/m³) for large ones. To convert, 1 g/cm³ = 1,000 kg/m³. Also, 1 litre is 1,000 cm³ and 1 mL is exactly 1 cm³.
Floating and sinking
Fresh water has a density of about 1 g/cm³ (1,000 kg/m³). Anything less dense floats and anything denser sinks. Ice at about 0.92 g/cm³ floats with most of its volume under the surface, while iron at about 7.9 g/cm³ sinks. Steel ships float because the hull encloses a lot of air, so the ship as a whole is less dense than the water it displaces.
The comparison here uses fresh water. Salt water is a little denser, about 1.03 g/cm³, so it holds objects up slightly better.
Typical densities
Approximate values at room temperature:
| Material | Density (g/cm³) |
|---|---|
| Air | 0.0012 |
| Ice | 0.92 |
| Water | 1.00 |
| Aluminium | 2.70 |
| Iron | 7.87 |
| Copper | 8.96 |
| Lead | 11.3 |
| Gold | 19.3 |
Common mistakes
- Mixing units. 500 g in 2 litres is 0.25 g/cm³, not 250. Convert litres to cm³ (×1,000) first, which this calculator does for you.
- Confusing mass and weight. Density uses mass. Weight depends on gravity.
- Forgetting density changes with temperature. Most materials expand when warm, becoming slightly less dense. Water is the famous exception near freezing.
Frequently asked questions
How do I calculate density?
Divide the mass by the volume. 500 g in 250 cm³ is 500 ÷ 250 = 2 g/cm³.
How do I find mass from density?
Multiply the density by the volume. 100 cm³ at 0.9 g/cm³ has a mass of 90 g.
How do I convert g/cm³ to kg/m³?
Multiply by 1,000. So 2.7 g/cm³ is 2,700 kg/m³.
How can I tell if something will float?
Compare its density with the liquid's. If it's lower than water's 1 g/cm³ (1,000 kg/m³) it floats in fresh water. The calculator shows this comparison.
Why do steel ships float?
A ship's hull encloses a large volume of air, so its overall density, including all that air, is less than water's, even though steel itself is much denser.
Formulas tested against hand-worked answers. Last reviewed 29 September 2026. These calculators do arithmetic only; they are not financial, tax or legal advice.