Sedimentation-Brownian crossover radius ($a_c=[3k_{B}T/(4\pi \Delta \rho g){]}^{1/4}$)

Setting the gravitational Péclet number to one gives the displayed particle-scale estimate. A macroscopic sample instead requires its height to be small compared with the sedimentation scale height. These different observational criteria give different size thresholds; “no sedimentation” is not an exact universal cutoff.