Buoyant force F_b
Upward force equal to the weight of displaced fluid.
Fluid mechanics · Hydrostatics
Buoyant force calculator
Calculate upward buoyancy F_b = ρgV from fluid density, actual displaced volume and gravity. Displaced volume may differ from the total volume of the object.
Created v1.0
By Thibaut Grzelak, Mechanical Analysis Engineer
02
Results
Relation and numerical substitution
F_b = ρgV—
Static fluid, uniform density and constant gravity; drag and surface tension are excluded.
01Formulas and symbols
Formulas used
F_b
F_b = ρ × g × Vρ: fluid density; g: gravity; V: displaced volume; F_b: buoyancy.02Assumptions and limits
Scope of validity
- Static fluid, uniform density and constant gravity; drag and surface tension are excluded.
03Validation example
Reference numerical case
- ρ = 1000 kg/m³, V = 0.002 m³ and g = 9.80665 m/s²: F_b = 1000 × 9.80665 × 0.002 = 19.6133 N (≈ 20 N).
04References
Technical references
FAQ
Which volume should I enter?
The volume actually displacing fluid. For a partly immersed object, only the part below the surface counts.
Does the result tell me whether the object floats?
No. Compare buoyancy with weight and other forces. Object mass is not an input in this calculation.
Does the formula apply in air?
Yes, using air density at the relevant conditions. The uniform-density assumption must remain suitable.
05Weight of displaced fluid
Pressure increases with depth. Its resultant on a body surrounded by fluid points upward and equals the weight of displaced fluid.
06Model boundaries
This is not a complete flotation or stability calculation. A sealed contact with the bottom, stratified fluid or surface tension may require another analysis.
07Fluid versus object
Enter the fluid density. Object density helps determine its weight, but does not enter ρgV directly.