Buoyancy Calculator

Enter the fluid density, submerged volume, and gravitational acceleration to calculate the buoyant force acting on an object. The Buoyancy Calculator applies Archimedes' principle (B = ρ × V × g) and tells you the buoyant force in Newtons, the weight of displaced fluid, and whether the object floats, sinks, or rests — just add the object's density to find out.

Select a preset to auto-fill fluid density, or choose Custom to enter your own.

kg/m³

Density of the fluid the object is submerged in. Water = 1000 kg/m³.

m³

Volume of the object that is submerged in the fluid (fully or partially).

kg/m³

Enter the object's density to determine if it floats, sinks, or rests. Leave blank to skip.

m/s²

Standard Earth gravity is 9.81 m/s². Change for other planets.

Results

Buoyant Force

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Mass of Displaced Fluid

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Weight of Displaced Fluid

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Object Status

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Net Force on Object

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Buoyant Force vs. Object Weight Breakdown

Frequently Asked Questions

What is buoyancy?

Buoyancy, also called upthrust, is an upward force exerted by a fluid on any object submerged in it. It acts in the opposite direction to gravity and is caused by pressure differences in the fluid at different depths. The deeper an object is submerged, the greater the pressure pushing it upward.

What is the buoyant force formula?

The buoyant force is calculated using Archimedes' principle: B = ρ × V × g, where ρ is the fluid density in kg/m³, V is the submerged volume of the object in m³, and g is gravitational acceleration (9.81 m/s² on Earth). The result is expressed in Newtons (N).

What causes buoyancy?

Buoyancy arises because fluid pressure increases with depth. The bottom surface of a submerged object experiences greater upward pressure than the top surface experiences downward pressure. This pressure difference creates a net upward force equal to the weight of the displaced fluid.

How do I know if an object will float or sink?

Compare the object's density to the fluid's density. If the object's density is less than the fluid's density, it floats. If it's greater, it sinks. If they're equal, the object remains neutrally buoyant (at rest). You can also compare the buoyant force to the object's weight directly.

What is the SI unit of buoyancy?

The SI unit of buoyancy (buoyant force) is the Newton (N), the same as any other force. It represents the upward force the fluid exerts on the submerged object, equivalent to the weight of the displaced fluid.

How much buoyancy do I need to float in water?

To float in water, the buoyant force must equal or exceed your body weight. Since the average human body density (around 985 kg/m³) is slightly less than fresh water (1000 kg/m³), most people naturally float — especially when the lungs are filled with air, which reduces average body density further.

Does buoyancy only apply to water?

No — buoyancy applies to any fluid, including gases. Hot air balloons float in air because the heated air inside has a lower density than the surrounding atmosphere, generating enough buoyant force to lift the balloon. The same Archimedes' principle applies universally to all fluids.

How can I estimate the buoyancy of a 1-litre water bottle?

A 1-litre bottle has a volume of 0.001 m³. Fully submerged in fresh water (ρ = 1000 kg/m³) with g = 9.81 m/s², the buoyant force is B = 1000 × 0.001 × 9.81 = 9.81 N, which equals the weight of 1 kg of water. Since an empty bottle weighs much less than this, it will float easily.

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