The Earth’s gravitational field acts upon colloidal particles. Therefore, if the colloidal particles are denser than the medium of suspension, they will sediment (fall to the bottom), or if they are less dense, they will cream (float to the top). Larger particles also have a greater tendency to sediment because they have smaller Brownian motion to counteract this movement.
The sedimentation or creaming velocity is found by equating the Stokes drag force with the gravitational force:
where
: is the Archimedean weight of the colloidal particles,
: is the viscosity of the suspension medium,
: is the radius of the colloidal particle,
and  is the sedimentation or creaming velocity.
The mass of the colloidal particle is found using:
where
: is the volume of the colloidal particle, calculated using the volume of a sphere ,
and  is the difference in mass density between the colloidal particle and the suspension medium.
By rearranging, the sedimentation or creaming velocity is:
There is an upper size-limit for the diameter of colloidal particles because particles larger than 1 μm tend to sediment, and thus the substance would no longer be considered a colloidal suspension.
The colloidal particles are said to be in sedimentation equilibrium if the rate of sedimentation is equal to the rate of movement from Brownian motion.