Buoyant Force Calculator

Calculate the upward buoyant force on a submerged object from fluid density, displaced volume, and gravity, then compare it to the object's weight to see if it floats or sinks.

Quick Facts

Formula
Fb = ρfluid × Vdisplaced × g
Buoyant force equals the weight of the fluid the object pushes out of the way (Archimedes' principle).
Common fluid densities
Fresh water 1000 kg/m³ · seawater ~1025 kg/m³
Air is about 1.2 kg/m³ at sea level, which is why buoyancy in air is usually negligible.

Your Results

Calculated
Buoyant Force
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Weight of fluid displaced
Object Weight
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Mass × gravity
Net Force
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Buoyant force minus weight
Buoyant Force (lbf)
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Same force in pounds-force

Ready

Enter the displaced volume, fluid density, object mass, and gravity, then press Calculate.

About Buoyant Force

Buoyant force is the upward push a fluid (a liquid or a gas) exerts on any object submerged or floating in it. Archimedes' principle describes it exactly: the buoyant force on an object equals the weight of the fluid the object displaces. This calculator applies that relationship directly to give the force in newtons, compare it against the object's own weight, and report the same force in pounds-force.

The formula

  • Fb = ρfluid × Vdisplaced × g — buoyant force equals fluid density times displaced volume times gravitational acceleration.
  • ρfluid is the fluid's density in kilograms per cubic meter (fresh water ≈ 1000 kg/m³, seawater ≈ 1025 kg/m³).
  • Vdisplaced is the volume of fluid pushed aside by the submerged part of the object. This calculator accepts it in liters and converts to cubic meters (1 L = 0.001 m³) before applying the formula.
  • g is gravitational acceleration — 9.81 m/s² on Earth, but the field is adjustable so you can check buoyancy on the Moon (1.62 m/s²) or elsewhere.

Reading the net force

Net force is buoyant force minus the object's weight (mass × g). A positive net force means the buoyant force is stronger than gravity pulling the object down, so the object accelerates upward and floats; it will settle at the point where the submerged volume shrinks enough for the two forces to balance. A negative net force means weight wins and the object sinks. When the two forces are equal, the object is neutrally buoyant and stays wherever it is placed, like a submarine holding depth.

Getting accurate results

  • Displaced volume is the volume of the submerged portion only — for a fully submerged object that is its whole volume, but for a floating object it is less than the total volume.
  • Fluid density changes with temperature and salinity, so use a value that matches your actual fluid, not just a textbook default.
  • Keep units consistent: this calculator expects volume in liters, density in kg/m³, mass in kilograms, and gravity in m/s², and reports force in newtons (with pounds-force as a reference conversion).

Frequently Asked Questions

What is the formula for buoyant force?
Buoyant force follows Archimedes' principle: Fb = fluid density x displaced volume x gravitational acceleration. It equals the weight of the fluid that the submerged object pushes out of the way, and it acts upward regardless of the object's own weight or shape.
Does buoyant force depend on how deep an object is submerged?
No, not for a liquid of essentially constant density. Once an object is fully submerged, the volume of fluid it displaces stays the same whether it is just below the surface or far deeper, so the buoyant force stays constant. Depth changes pressure, not the displaced volume.
Why does a steel ship float when a solid block of steel sinks?
Buoyant force depends on the volume of water displaced, not on the material alone. A ship's hull encloses a large volume of air, so the hull-plus-air shape displaces far more water than a solid steel block of the same mass. That larger displaced volume produces enough buoyant force to support the ship's full weight.
How do I know if an object will float or sink?
Compare the buoyant force at full submersion to the object's weight. If the buoyant force is greater than the weight, the object floats and rises until only part of it is submerged. If the buoyant force is less than the weight, the object sinks. If the two are equal, the object is neutrally buoyant and stays suspended.

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