Buoyant Force Calculator
The buoyant force is the upward push a fluid exerts on any object placed in it. Archimedes' principle states that this force equals the weight of the fluid the object displaces. Enter the fluid density, the volume of fluid displaced, and the local gravitational acceleration to find the buoyant force in newtons, along with the displaced fluid mass and its weight. These three quantities are equal because the buoyant force is exactly the weight of displaced fluid.
Buoyant force formula
F = rho * V * g
where rho = fluid density (kg/m3)
V = displaced volume (m3)
g = gravitational acceleration (m/s2)
Displaced mass = rho * V
Displaced weight = rho * V * g (equals F)
Archimedes' principle: a body wholly or partly immersed in a fluid is buoyed up by a force equal to the weight of the fluid it displaces. The buoyant force depends only on the fluid and the displaced volume, never on the object's own mass.
Worked example
A block displaces 0.05 m3 of fresh water (density 1,000 kg/m3) with gravity 9.81 m/s2. Displaced mass = 1,000 * 0.05 = 50 kg. Buoyant force = 50 * 9.81 = 490.50 N. The block experiences an upward push of 490.50 newtons regardless of what it is made from.
Buoyant force: frequently asked questions
What is the formula for buoyant force?
Buoyant force equals fluid density times displaced volume times gravitational acceleration: F = rho * V * g. This is Archimedes' principle: the upward buoyant force equals the weight of the fluid the object displaces.
What density should I use for water?
Fresh water at 4 degrees Celsius has a density of 1,000 kg/m3, the value used as the default here. Sea water is denser at roughly 1,025 kg/m3. The density field is editable so you can enter the exact value for your fluid and temperature.
Does the object's own weight matter for buoyant force?
No. The buoyant force depends only on the displaced fluid, not on the object's mass or material. To find whether the object floats or sinks, compare the buoyant force to the object's weight separately.
What value of gravity should I use?
Standard gravity is 9.80665 m/s2, often rounded to 9.81 m/s2, which is the editable default. On other planets or for high-precision work you can enter a different local value.
Sources
- NIST: standard acceleration of gravity (9.80665 m/s2).
- NIST: SI units. Archimedes' principle is a standard result of classical fluid statics.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.