🛟Buoyancy Calculator

About this tool

Enter the object's volume and mass and choose a fluid (or type a density). The tool shows the buoyant force when fully submerged, whether it floats and how deep, how much extra load it can carry, or its apparent weight if it sinks.

Floating and sinking

Archimedes' principle: a body in a fluid feels an upward force equal to the weight of the fluid it displaces, F_b = ρ_fluid × V × g. If the object's average density is lower than the fluid's, it floats, sinking only until it displaces its own weight, so the fraction submerged = object density ÷ fluid density. Ice at 917 kg/m³ floats about 92% submerged in fresh water and about 89% in seawater, the tip of the iceberg. A 1 litre, 0.5 kg object floats half-submerged and can carry 0.5 kg more before going under. Denser objects sink but weigh less in the fluid: a 1 litre block of aluminium (2.7 kg) has an apparent weight of 1.7 kg underwater, which is how divers and salvage teams use lift bags. Seawater's higher density lets ships float slightly higher than in rivers, and helium balloons rise because they're lighter than the air they displace. Honest limits: this assumes a rigid object of known volume; boats float because their hull encloses air, and floating stability is a separate calculation. The density calculator and the pool volume calculator are related.

Frequently asked questions