The density formula
Density measures how much mass is packed into a volume: ρ = m / V. A 100 g object filling 50 cm³ has a density of 2 g/cm³. Water is 1 g/cm³, so anything denser than that sinks. The Greek letter ρ (rho) is the standard symbol for density.
Density is an intensive property: it does not depend on how much of the substance you have. Cut that 100 g sample in half and you have 50 g in 25 cm³, which is still 2 g/cm³. For an irregular object the harder half of the job is the volume, not the mass.
How to use this calculator
Enter the mass in grams and the volume in cubic centimeters. The result is grams per cubic centimeter (g/cm³), which is numerically equal to kg per liter. Keep units consistent; mixing grams with liters will give a wrong figure.
For an irregular solid, the usual laboratory method is displacement: drop the object into a measuring cylinder of water and read off the rise in level. A rise of 50 mL equals 50 cm³, so a 100 g object gives the 2 g/cm³ above. Trapped air bubbles are the classic source of error, since they inflate the measured volume and make the object look less dense than it is. Density is also what links a column of fluid to the pressure it exerts at the bottom.
Common densities
For reference: water ≈ 1 g/cm³, aluminum ≈ 2.7 g/cm³, iron ≈ 7.9 g/cm³, and lead ≈ 11.3 g/cm³. Density helps identify materials and predict whether they float. It also feeds into gas-law work — see the ideal gas law calculator for gases.
Comparing a measured value against that list is a quick identity check on an unknown sample. Bear in mind that a hollow or porous object has a much lower average density than the solid material it is made from — which is exactly how a steel ship floats.
Frequently asked questions
- How do I calculate density?
- Divide mass by volume: ρ = m / V. 100 g in 50 cm³ is 2 g/cm³.
- What is the density of water?
- About 1 g/cm³ (1,000 kg/m³) at room temperature.
- What units does density use?
- Grams per cubic centimeter (g/cm³) here, equal to kilograms per liter; SI uses kg/m³.
- Will an object float?
- If its density is less than the fluid's it floats; denser objects sink. Anything under 1 g/cm³ floats in water.
- How do I convert g/cm³ to kg/m³?
- Multiply by 1,000. A density of 2 g/cm³ is 2,000 kg/m³, because a cubic metre holds a million cubic centimetres while a kilogram is a thousand grams. Going the other way, divide kg/m³ by 1,000.