🛟Buoyancy Calculator
Find the buoyant force on a submerged object and see whether it sinks or floats.
Free Buoyancy Calculator
This buoyancy calculator applies Archimedes' principle — the buoyant force on a submerged object equals the weight of fluid it displaces: F_b = ρ_fluid × V × g. Enter the fluid density, the object's volume, and its mass, and the calculator finds the buoyant force, the object's weight, and tells you whether it sinks, floats, or hovers neutrally.
An object floats when the buoyant force exceeds its weight — equivalently, when its average density is less than the fluid's density. For floating objects, the calculator also shows the fraction of the object's volume that ends up submerged, which equals the ratio of object density to fluid density.
Useful for physics coursework covering fluid mechanics, ship and submarine design, or just satisfying curiosity about why steel ships float. Free, runs entirely in your browser.
About the Buoyancy Calculator
Features
Fluid presets
Fresh water, seawater, air, mercury, oil, or a custom density.
Sink/float verdict
A clear result showing whether the object floats, sinks, or hovers.
Submerged fraction
For floating objects, see exactly how much volume stays underwater.
Instant, private
Runs entirely in your browser. No data is sent anywhere.
Frequently Asked Questions
What is Archimedes' principle?
Archimedes' principle states that the buoyant force on a submerged object equals the weight of the fluid it displaces: F_b = ρ_fluid × V × g.
How do I know if an object will sink or float?
Compare the buoyant force to the object's weight. If the buoyant force is greater, it floats; if less, it sinks; if equal, it's neutrally buoyant. Equivalently, compare the object's average density to the fluid's density.
Why do steel ships float when steel is denser than water?
A ship's hull encloses a large volume of air, so the ship's overall average density (steel plus air) is less than water's density, even though solid steel alone would sink.
What does 'submerged fraction' mean?
For a floating object, it's the percentage of its volume below the fluid's surface, equal to the object's density divided by the fluid's density.
What is apparent weight?
Apparent weight is how heavy a fully submerged object 'feels' — its actual weight minus the buoyant force acting on it. This is why objects feel lighter underwater.
Does buoyant force depend on depth?
No, for an incompressible object fully submerged, buoyant force only depends on the fluid's density, the object's volume, and gravity — not how deep it is.
What units does this calculator use?
SI units: kg/m³ for density, m³ for volume, kg for mass, and the results are given in newtons (N) for force.
Why can I choose different fluids?
Buoyant force depends directly on fluid density, so the same object behaves very differently in water, seawater, oil, mercury, or air — the fluid presets let you compare quickly.
Can this calculator be used for gases like air?
Yes — buoyancy applies to any fluid, including gases. Selecting air as the fluid shows why a helium balloon rises: its average density is lower than air's.
Is this calculator free to use?
Yes, completely free with no sign-up, and it runs entirely in your browser.