Buoyancy Calculator
Apply Archimedes’ principle to find buoyant force and whether an object floats.
Please note: Results use idealised models — point masses, no air resistance, ideal gases and uniform materials. Real experiments deviate. Use these for study and estimation, not for engineering sign-off.
What the Buoyancy Calculator does
Archimedes’ principle says the upward force on a submerged object equals the weight of fluid it displaces. Whether something floats therefore comes down to a comparison of densities — and if it floats, it sinks exactly far enough to displace its own weight.
Formula
F_buoyant = ρ_fluid × V_displaced × gFloats when ρ_object < ρ_fluidFraction submerged = ρ_object ÷ ρ_fluidApparent weight = Weight − Buoyant force
Inputs explained
| Input | Unit | Required | Notes |
|---|---|---|---|
| Object mass | number | Yes | — |
| Object mass unit | one of 6 options | Yes | — |
| Object volume | number | Yes | — |
| Object volume unit | one of 6 options | Yes | — |
| Fluid | one of 13 options | Yes | — |
| Gravitational acceleration | m/s² | Optional | Standard gravity on Earth is 9.80665 m/s². The Moon is 1.62, Mars 3.72. Accepts 0 or more. |
How to use it
- Choose Object mass unit and Object volume unit.
- Enter Object mass and Object volume.
- Optionally add Gravitational acceleration.
- Select Calculate.
Worked example
A 10 kg object of 20 litres volume placed in fresh water.
- Mass
- 10 kg
- Volume
- 20 L
- Fluid
- Water (1000 kg/m³)
Density 500 kg/m³, half of water’s, so it floats with 50% submerged. Fully submerged it would feel 196.1 N of lift against 98.1 N of weight, and it can carry another 10 kg before sinking.
Frequently asked questions
Why does an iceberg show so little above water?
Ice is 917 kg/m³ against seawater’s 1,025, so the submerged fraction is 917/1025 = 89.5%. Only about a tenth is visible.
Do you weigh less underwater?
Your apparent weight drops because buoyancy pushes up, but your mass is unchanged. A person near water’s density feels almost weightless.