Buoyancy Calculator
Will it float? Find the upthrust and the fraction submerged.
Your numbers
Your results
Upthrust if fully submerged (N)
Upthrust if fully submerged (N)
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Weight (N)
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Result
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Fraction submerged when floating
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Buoyancy Calculator by TheCalcTools
How the Buoyancy Calculator works
Enter the object’s mass and volume and pick the fluid.
Archimedes’ principle says the upthrust equals the weight of the fluid displaced.
The object floats if its average density is below the fluid’s.
The formula
F(up) = ρ(fluid) × V × gfraction submerged = ρ(object) ÷ ρ(fluid)
Worked example
Using the default values shown in the calculator:
| Object mass (kg) | 20 |
|---|---|
| Object volume (litres) | 25 |
| Fluid | Fresh water (1000 kg/m³) |
- Object density = 20 kg ÷ 0.025 m³ = 800 kg/m³, below water.
- Floats: about 80% of it is submerged.
- Full-submersion upthrust = 245.2 N against a weight of 196.1 N.
Result:
| Upthrust if fully submerged (N) | 245.17 |
|---|---|
| Weight (N) | 196.13 |
| Result | Floats |
| Fraction submerged when floating | 80.0% |
Frequently asked questions
Why do steel ships float?
Their hull encloses a large volume of air, so the average density of the whole ship is below that of water.
Why is it easier to float in sea water?
Salt raises the density, so less volume needs to be submerged to displace the object’s weight.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.