CalcLibrary

Buoyancy Calculator

Estimate whether an object floats in a chosen fluid, how much of it sits below the surface, and how much mass it can still carry before full submersion.

activeEquation
Examples

12 kg object, 0.05 m³ displacement, water at 1000 kg/m³. It floats with 38 kg of remaining payload margin and about 24% submergence.

Buoyancy verdict
Floats
Maximum buoyant force at full displacement
490.5 N
Object weight
117.72 N
Submerged volume at floating equilibrium
0.012 m³
Submerged fraction at floating equilibrium
24%
Maximum supported mass at full displacement
50 kg
Remaining payload margin before full submersion
38 kg

The object can float. In steady floating equilibrium, buoyant force matches the object weight; the larger full-displacement buoyant force shown above is the available ceiling that sets payload margin.

Static buoyancy estimate only. This page does not predict stability, hull shape effects, trapped air behavior, trim, waves, dynamic drag, or safety certification.

Was this useful?

Examples

How It Works

Formula

Fb,max⁡=ρfgVmax⁡F_{b,\max} = \rho_f g V_{\max}

W=mgW = m g

Vsub=mρfV_{sub} = \frac{m}{\rho_f}

mmax⁡=ρfVmax⁡m_{\max} = \rho_f V_{\max}

mpayload=mmax⁡−mm_{payload} = m_{\max} - m

Variables

Fb,max⁡F_{b,\max}

Maximum buoyant force at full displacement(N or lbf)

WW

Object weight(N or lbf)

VsubV_{sub}

Submerged volume needed while floating(m³, L, or ft³)

mmax⁡m_{\max}

Maximum total supported mass at full displacement(kg or lb)

mpayloadm_{payload}

Remaining payload mass before full submersion(kg or lb)

ρf\rho_f

Fluid density(kg/m³, g/cm³, or lb/ft³)

gg

Gravitational acceleration(m/s² or ft/s²)

Vmax⁡V_{\max}

Maximum external displacement volume(m³, L, or ft³)

mm

Object mass(kg or lb)

Choose whether you know object mass or average object density. Enter the maximum displacement volume, the fluid density, and optionally a different gravity value. The calculator converts the chosen units into one physics basis, compares the object weight with the maximum full-displacement buoyant force, and then either reports floating equilibrium or quantifies the shortfall.

The planning model is simple and static. First, the maximum available buoyant force is found from Fb,max⁡=ρfgVmax⁡F_{b,\max} = \rho_f g V_{\max}. The object weight is W=mgW = m g. If Fb,max⁡F_{b,\max} is at least as large as WW, the object can float. Its steady floating state does not use the full buoyant-force ceiling; it only needs enough displaced fluid to satisfy ρfgVsub=mg\rho_f g V_{sub} = m g, so Vsub=m/ρfV_{sub} = m / \rho_f. The same full-displacement ceiling also sets the maximum supported mass mmax⁡=ρfVmax⁡m_{\max} = \rho_f V_{\max} and the remaining payload margin mpayload=mmax⁡−mm_{payload} = m_{\max} - m.

Frequently Asked Questions

01What does this buoyancy calculator actually estimate?
It estimates static buoyancy from average object mass or density, external displacement volume, fluid density, and gravity. It answers whether full displacement can support the object and, if so, how much fluid it must displace at equilibrium.
02Why is maximum buoyant force different from the steady floating force?
Maximum buoyant force is the upper limit at full submersion: rho_f × g × Vmax. A floating object usually displaces less than that. In steady floating equilibrium, buoyant force only rises until it matches the object’s weight.
03Why does the calculator ask for external displacement volume?
Buoyancy depends on how much fluid the object can push aside, not just on the solid material inside it. A sealed container or foam insert can have a large external volume relative to its mass, which is why it may float even if some parts are dense.
04What does payload margin mean here?
Payload margin is the extra mass the object could still carry before it reaches full submersion in the chosen fluid. It is the difference between maximum supported mass and the object’s own mass.
05What does this calculator not predict?
It does not predict stability, hull shape effects, trapped air behavior, trim, waves, dynamic drag, or safety certification. It is a static buoyancy estimate only.

All calculators