Calculate buoyant force for spheres, cubes, cylinders, and boxes in any fluid. Supports partial submersion, multiple fluids, and weight capacity analysis.
The buoyant force is the net upward force exerted on an object immersed in a fluid, equal to the weight of the fluid displaced. This fundamental force — described by Archimedes' principle — determines whether objects float, how deep they sit, and how much additional weight they can carry.
This calculator computes buoyant force for five different object shapes (sphere, cube, cylinder, rectangular box, or custom volume) in any fluid. A partial-submersion slider lets you analyze objects that are only partially immersed, which is common in real-world scenarios like pontoons, floats, and partially loaded vessels.
A comparison table shows the buoyant force the same object would experience across eight different fluids — from air to mercury — demonstrating the dramatic effect of fluid density on buoyancy. Presets cover balloons in air, anchors in seawater, pontoons, and more. Check the example with realistic values before reporting. Use the steps shown to verify rounding and units. Cross-check this output using a known reference case.
Computing buoyant force manually requires calculating volumes for different geometries and keeping track of units. This calculator handles five shapes, any fluid, and partial submersion in one unified tool.
The multi-fluid comparison table is especially valuable for engineering comparisons — seeing how the same object behaves in water vs. seawater vs. oil vs. mercury provides immediate design insight.
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.
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.