Qualitatively, we can say that the buoyant force exerted by a fluid on an object is proportional to the volume of fluid displaced by the object.

Quantitatively: F_b = ρ_fluidgV_disp

This is known as Archimedes' principle.

ρ_fluid represents the density of the fluid.
V_disp represents the volume of fluid displaced by the object.

Note that density is equal to mass divided by volume.

ρ

=

m V