Density Calculator
Calculate density, mass or volume, and check whether something floats.
Please note: Results come from idealised models that assume clean, standard conditions. Real measurements deviate, and published constants carry their own tolerances. Use these for study and estimation, not for engineering sign-off.
What the Density Calculator does
Density is mass per unit volume — how much matter is packed into a given space. It decides whether something floats, and comparing it against water gives specific gravity, the number most float and buoyancy questions actually turn on.
Formula
ρ = m ÷ Vm = ρ × VV = m ÷ ρSpecific gravity = ρ_object ÷ ρ_water
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Solve for | one of 3 options | Yes | — |
| Mass | number | In some modes | Shown Solve for is Density, or Solve for is Volume. |
| Mass unit | one of 6 options | In some modes | Shown Solve for is Density, or Solve for is Volume. |
| Volume | number | In some modes | Shown Solve for is Density, or Solve for is Mass. |
| Volume unit | one of 6 options | In some modes | Shown Solve for is Density, or Solve for is Mass. |
| Density | number | In some modes | Shown Solve for is Mass, or Solve for is Volume. |
| Density unit | one of 4 options | In some modes | Shown Solve for is Mass, or Solve for is Volume. |
| Compare against | one of 13 options | Optional | Used for the specific gravity and float test. |
How to use it
- Choose Solve for and Compare against.
- Fill in the remaining inputs the form shows for your choice.
- Select Calculate.
Worked example
An object of 500 g occupying 200 cm³.
- Mass
- 500 g
- Volume
- 200 cm³
ρ = 0.5 kg ÷ 0.0002 m³ = 2,500 kg/m³, or 2.5 g/cm³. Specific gravity 2.5, so it sinks in water.
Frequently asked questions
Why does a steel ship float when steel sinks?
Because the hull encloses a large volume of air. It is the average density of the whole ship — steel plus air — that matters, and that comes out below water’s.
What is specific gravity?
Density divided by water’s density, so it has no units. Below 1.0 floats, above 1.0 sinks, and the value also gives the fraction of a floating object that sits underwater.