Calculate the buoyant force (Archimedes' principle) from the fluid density and the object's volume and mass, and see whether it floats or sinks.
Last updated: November 8, 2026
Archimedes' principle
By Archimedes' principle, an object in a fluid is pushed up by a force equal to the weight of the fluid it displaces: • F = ρ_fluid × V × g • ρ_fluid fluid density (kg/m³), V submerged volume (m³), g = 9.81 m/s² Example: an object of 10 litres (0.01 m³) fully under water gets 1,000 × 0.01 × 9.81 ≈ 98.1 N of buoyancy. If it has a mass of 7 kg, its weight is 68.6 N; buoyancy wins, so it floats with 70% of its volume under water. In short: an object less dense than the fluid floats, a denser one sinks.
Common questions about buoyancy
F = ρ × V × g: fluid density times submerged volume times gravitational acceleration.
Other tools you may find useful
Fresh water 1,000, seawater ≈ 1,025.
In litres, assumed fully submerged.
In kilograms.