Physics
Archimedes principle
The buoyant force equals the weight of the fluid pushed aside, so only the displaced volume and the fluid's density matter.
The Formula
F = fluid density x volume x g
The buoyant force equals the weight of the fluid pushed aside, so only the displaced volume and the fluid's density matter.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| F | Buoyant force | N | Upward force from the fluid. |
| rho | Fluid density | kg/m3 | Mass per cubic metre of the fluid. |
| V | Displaced volume | m3 | Volume of fluid pushed out of the way. |
| g | Gravity | m/s2 | Acceleration due to gravity, about 9.81. |
What Each Symbol Means
FN
Buoyant force
Upward force from the fluid.
rhokg/m3
Fluid density
Mass per cubic metre of the fluid.
Vm3
Displaced volume
Volume of fluid pushed out of the way.
gm/s2
Gravity
Acceleration due to gravity, about 9.81.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate buoyancy page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate Buoyancy, filed under Science. Every number the guide produces comes from substituting into this one line.