Buoyancy Calculator
Calculate buoyant force, apparent weight, and whether an object floats or sinks using Archimedes' principle. Includes submerged volume fraction and displacement tonnage.
Buoyant Force (N)
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Object Weight (N) —
Float or Sink? —
Apparent Weight in Fluid (N) —
Extended More scenarios, charts & detailed breakdown ▾
Float or Sink?
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Density Ratio (obj/fluid) —
Professional Full parameters & maximum detail ▾
Ship/Boat Displacement
Displacement Volume (m³) —
Draft Depth (m) —
Displacement Tonnage (tonnes) —
Fluid Info
Fluid Density Used —
How to Use This Calculator
- Enter Object Volume (cm³), Object Mass (g), and Fluid Density (g/cm³, water=1.0).
- See buoyant force, weight, apparent weight, and float/sink determination.
- Use the Float/Sink tab to compare densities directly.
- Use the Submerged Volume tab to find what fraction of a floating object is underwater.
- The Professional tab covers boat draft depth and displacement tonnage.
Formula
Buoyant Force: F_b = ρ_fluid × V × g
Floats if: ρ_object < ρ_fluid | Fraction submerged: ρ_object / ρ_fluid
Example
Object 500 cm³, 400 g in water: F_b = 1000×5×10⁻⁴×9.81 ≈ 4.91 N, Weight = 3.92 N → Floats.
Frequently Asked Questions
- An object submerged in a fluid experiences an upward buoyant force equal to the weight of the fluid it displaces. F_b = ρ_fluid × V_displaced × g.
- An object floats if its average density is less than the fluid density. If ρ_object < ρ_fluid, the object floats. It floats at a depth where displaced fluid weight equals object weight.
- Fraction submerged = ρ_object / ρ_fluid. For wood with ρ=0.6 g/cm³ in water (1.0 g/cm³): 60% is submerged, 40% above water.
- Apparent weight = actual weight − buoyant force. When fully submerged, an object feels lighter by the weight of displaced fluid. A 400g rock in water appears to weigh less.
- Ship displacement = mass of water displaced by the hull. A ship displaces water equal to its own mass. This is expressed in tonnes: 1 displacement tonne = 1000 kg of sea water.