Calculate buoyant force for spheres, cubes, cylinders, and boxes in any fluid. Supports partial submersion, multiple fluids, and weight capacity analysis.
Buoyant force is the upward force a fluid exerts on an immersed object, and its magnitude equals the weight of the displaced fluid. That relationship is the core of Archimedes' principle and explains why some objects float while others sink.
This calculator works with several common shapes, or a custom volume, and it can also handle partial submersion. That makes it useful for pontoons, floats, hull sections, balloons, anchors, and any situation where only part of the object is in the fluid.
The comparison table shows how the same object behaves in different fluids, from air to mercury, so the effect of density is easy to see at a glance.
Buoyancy problems are mostly geometry plus fluid density, but those pieces become tedious to combine by hand once the object shape or submersion changes. Putting the shapes, fluids, and comparison table together keeps the calculation easier to reason about.
Buoyant force F_b = ρ_fluid × V_displaced × g. V_displaced = V_total × (% submerged / 100). Weight supported = F_b / g.
Result: Buoyant force = 2880 N, supports 293 kg
A pontoon cylinder (0.5 m diameter, 3 m long) half-submerged in water displaces 294 liters, producing 2,880 N of buoyant force — enough to support about 293 kg.
Buoyant force calculations are critical in offshore engineering (oil platform design), marine engineering (hull and ballast design), civil engineering (bridge pontoons), and aerospace (lighter-than-air craft). The oil industry uses buoyancy to design tension-leg platforms and spar buoys that float at engineered depths.
Life jackets work by adding buoyant volume to the human body, lowering average density below water. Swimming pool floating aids, inflatable rafts, and fishing bobbers all exploit buoyancy. Even cooking — testing egg freshness by floating in water — uses buoyancy principles.
Buoyant force scales with the cube of linear dimensions (since volume ∝ length³). Doubling an object's size increases buoyant force eightfold. This is why large ships can carry enormous loads — the displaced water volume grows much faster than the hull weight.
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Buoyant force is the upward push a fluid exerts on any object placed in it. It equals the weight of the displaced fluid, as stated by Archimedes' principle: F_b = ρ_fluid × V_displaced × g.
Shape determines volume, which determines the amount of displaced fluid. For the same volume, shape does not matter — only the displaced fluid volume determines buoyant force.
Many real-world objects are only partially submerged — boats, floating platforms, buoys, and ice. The partial submersion setting lets you calculate buoyant force for the actual immersed portion.
Air has a density of only 1.225 kg/m³ at sea level, so buoyant force in air is very small. However, for light objects like helium balloons, this small force is enough to cause them to rise.
Set submersion to 100% and read the "Weight Supported" value. This is the maximum total mass (float + cargo) that can be supported before the object is fully submerged.
Mercury has a density of 13,546 kg/m³ — about 13.5 times denser than water. Since buoyant force is proportional to fluid density, the same object experiences 13.5× more buoyancy in mercury.