In a colloid, 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. For dilute colloids, this is described using the Laplace-Perrin distribution law:
where
 is the colloidal particle volume fraction as a function of vertical distance  above reference point ,
 is the colloidal particle volume fraction at reference point ,
 is the buoyant mass of the colloidal particles,
 is the standard acceleration due to gravity,
is the Boltzmann constant,
 is the absolute temperature,
and  is the sedimentation length.
The buoyant mass is calculated using 
where  is the difference in mass density between the colloidal particles and the suspension medium, and  is the colloidal particle volume found using the volume of a sphere ( is the radius of the colloidal particle).