Buoyant Force Calculator — Float or Sink?
Enter the fluid density, the object's density and volume, and gravitational acceleration to get the buoyant force, the object's weight, the net force, and whether the object floats or sinks — plus the fraction of a floating object that sits below the surface.
Fluid
kg/m³
m³
m/s²
Downward net force; object sinks (weight exceeds buoyant force)
- 1
Buoyant force F_b = ρ_fluid × V × g
1,000 × 0.001 × 9.81 = 9.81 - 2
Object weight W = ρ_obj × V × g
2,700 × 0.001 × 9.81 = 26.487 - 3
Net force = W − F_b
26.487 − 9.81 = 16.677Positive = net downward (sinks); zero or negative = floats.
How does this calculator work?
Buoyant force equals fluid density × volume × g. Compare to the object's weight (object density × volume × g). If buoyant force ≥ weight, the object floats with a submerged fraction of ρ_object / ρ_fluid. If weight > buoyant force, the net downward force is the difference and the object sinks.
Formula
How this is calculated
This calculator combines Archimedes' principle with Newton's second law to find out what actually happens when an object is placed in a fluid. The buoyant force is F_b = ρ_fluid × V × g (fluid density times volume times gravity). The object's true weight is W = ρ_object × V × g. The net force on the object is the difference F_net = W − F_b.
If F_net > 0 (object denser than fluid), gravity wins and the object sinks. If F_net ≤ 0 (object less dense or equal to the fluid), the buoyant force can support the full weight, so the object floats. When floating, only a fraction of the object (ρ_object / ρ_fluid) is submerged — that is why a wooden block (≈ 600 kg/m³) floats about 60 % submerged in fresh water.
The densities in the dropdown are standard reference values at around 20 °C. Real-world results can vary with temperature, salinity, or impurities in the fluid.
Frequently asked questions
An object floats when its average density is less than or equal to the fluid's density. This makes the buoyant force (at full submersion) greater than or equal to the object's weight, so the net downward force is zero or negative — the fluid can hold it up.
For a floating object, the submerged fraction equals the object's density divided by the fluid's density: f = ρ_object / ρ_fluid. An iceberg with density ≈ 917 kg/m³ in sea water at 1025 kg/m³ has about 89 % submerged — which is where the phrase 'tip of the iceberg' comes from.
A solid block of steel sinks because its density (≈ 7800 kg/m³) far exceeds water. But a ship is a hollow shell — its average density (total mass divided by total enclosed volume including air) is much less than water, so the ship as a whole floats.
Also known as
TG we-Calculate Editorial Team. (2026). Buoyant Force Calculator — Float or Sink? [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/buoyant-force-calculator
TG we-Calculate Editorial Team. "Buoyant Force Calculator — Float or Sink?." TG we-Calculate. 2026. https://we-calculate.com/calculator/buoyant-force-calculator.
TG we-Calculate Editorial Team, "Buoyant Force Calculator — Float or Sink?," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/buoyant-force-calculator
@misc{wecalculate_buoyant_force_calculator, title = {Buoyant Force Calculator — Float or Sink?}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/buoyant-force-calculator}}, year = {2026}, note = {TG we-Calculate} }
Did this calculator help you?