Archimedes' Principle Calculator

The buoyant force on a submerged object equals the weight of fluid it displaces. Discovered by Archimedes ~250 BCE.

When its average density is less than the fluid's density. The submerged fraction equals object density / fluid density.

Weight minus buoyant force - what a scale reads when the object is submerged. A 100 N object losing 30 N of buoyancy weighs 70 N apparent.

Its true weight does not change, but buoyancy cancels part of it while submerged, so a scale reads the apparent weight = true weight minus buoyant force. A 300 kg steel engine block (volume about 0.038 m³) displaces roughly 38 kg of water, so raising it through the water takes only about 262 kgf. The moment it breaks the surface the buoyancy disappears and the full 300 kgf returns.

Because a ship is mostly hull cavity, not solid steel. What matters is average density: total mass divided by the whole volume the hull pushes aside, including the air inside. A steel hull that encloses enough empty space has an average density below 1000 kg/m³, so it floats. If the hull floods, that air is replaced by water, the average density climbs above water's, and the ship sinks.