Buoyancy Calculator
Calculate the buoyant force on a submerged object from the fluid density and displaced volume using Archimedes’ principle.
How it works
F_b = ρ·V·g · displaced mass = ρ·V
Archimedes’ principle states that the upward buoyant force on a submerged object equals the weight of the fluid it displaces. It depends on the fluid’s density and the volume submerged, not on the object’s own weight. If this buoyant force exceeds the object’s weight it floats; if less, it sinks. This is why a steel ship floats but a steel bolt does not — the ship displaces far more water.
Worked example
An object with 0.05 m³ submerged in water (ρ = 1,000 kg/m³, g = 9.81) displaces 50 kg of water and feels a buoyant force of 1,000 × 0.05 × 9.81 ≈ 490.5 N upward.
Sources: Archimedes' principle — Wikipedia
Frequently asked questions
Why do objects feel lighter in water?
The buoyant force pushes up on the submerged object, partly cancelling its weight. The apparent weight is the true weight minus the buoyant force, which is why lifting things underwater feels easier.
What decides whether something floats?
Compare average densities. If the object is less dense than the fluid, it displaces enough fluid to balance its weight before fully submerging, so it floats. Denser objects sink.
Does buoyancy depend on depth?
For an incompressible fluid, no — the buoyant force depends on the displaced volume and fluid density, which stay the same at any depth. In compressible fluids like air it changes slightly as density varies.
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Educational estimate. Check the formula and units for your exact case.