Buoyancy Calculator

The upward force on a body in a fluid equals the weight of the fluid it displaces: F_b = ρ_fluid · V_displaced · g. Nothing else enters — not the body's material, not its shape, not the depth (in an incompressible fluid). A fully submerged body displaces its own volume; a floating one displaces only as much as its own weight, which is why the two cases give different answers from the same formula. Apparent weight on a scale in the fluid is the real weight minus the buoyant force.

A body floats when its average density is below the fluid's, and it then settles until the displaced weight equals its own — so the submerged fraction is exactly ρ_body ÷ ρ_fluid. Pine at 500 kg/m³ in fresh water sits half under; ice at 917 in seawater at 1 025 sits with 89 % under, which is the iceberg figure. The reserve load is how much more mass it can take before the deck goes under: (ρ_fluid − ρ_body) × V. Equal densities give neutral buoyancy, which is stable only for an incompressible body — a wetsuit or a swim bladder compresses as it goes deeper, displaces less, and sinks faster.

Static fluid at rest, no surface tension (which floats a needle and a water strider), no viscosity or drag — the sinking acceleration given is the initial one, before drag builds up, and the drag tool takes it from there. Most importantly the page says nothing about *stability*: whether a floating body stays upright depends on where its centre of gravity sits relative to the centre of buoyancy as it heels, and that is naval architecture, not Archimedes. Fluid densities are yours: fresh water is about 997 kg/m³ at 25 °C, seawater 1 025, air 1.225. Nothing leaves the browser; the same four anonymous usage counts as the rest of the site apply.