🛟 Buoyancy Calculator (Archimedes)
Enter the fluid density and displaced volume to get the buoyant force — add the object's mass to see whether it floats or sinks.
Buoyant force
490.33 N
Object weight 392.27 N →
Floats ⬆
Archimedes' principle: the upward buoyant force equals the weight of the displaced fluid, F = ρ·V·g. An object floats when that force is at least its own weight (i.e. its average density is below the fluid's). 🔒 In your browser.
How the buoyancy calculator (archimedes) works
Archimedes' principle says the upward buoyant force on an object equals the weight of the fluid it displaces: F = ρ_fluid × V × g, where ρ is the fluid's density, V the displaced volume and g gravity (9.81 m/s²). If you also enter the object's mass, the tool compares its weight (m × g) to the buoyant force: it floats when the buoyant force from its fully submerged volume is at least its weight — equivalently, when its average density is less than the fluid's.
Density presets are built in (fresh water 1000, seawater 1025, oil ~900, mercury 13534 kg/m³). A ship of steel floats because its shape displaces a large volume of water — its average density, including the air inside, is below water's. The same steel as a solid block sinks.
Frequently asked questions
What is Archimedes' principle?
The buoyant (upward) force on a body in a fluid equals the weight of the fluid it displaces: F = ρ·V·g. It explains why objects feel lighter in water and why some float.
How do I calculate buoyant force?
Multiply the fluid's density by the displaced volume and by g: F = ρ × V × 9.81. One cubic metre submerged in water (1000 kg/m³) experiences about 9,807 N of buoyancy.
Will an object float or sink?
It floats if its average density is less than the fluid's — equivalently, if the buoyant force when fully submerged is at least its weight. Enter the object's mass and the tool tells you which.
Why does a steel ship float but a steel bar sinks?
A ship's hull encloses a large volume of air, so it displaces a lot of water for its weight — its average density is below water's. A solid steel bar displaces only its own small volume, so it sinks.
Does buoyancy work in air?
Yes — air (density ~1.2 kg/m³) exerts a small buoyant force, which is why helium and hot-air balloons rise. Set the fluid density to air to explore it, though the forces are much smaller than in water.