The relevant density of dispersion depends on the dimensionless size r of the submerged body. It is the fluid density rho(f), when r < 1. It is the mixture density rho(m), when r > R, about 10, say. It lies somewhere between rho(f) and rho(m), when 1 <= r <= R. Within this intermediate range, it can be expressed as a weighted sum (1 - f) rho(f) + f rho(m) of the fluid and mixture densities. The weight function f is an element of (0, 1) depends on the body size r. Based on the data taken from literature, it is found: f (r) = 0.1635(r - 1), which gives R = 7.116. When we apply the mixture density concept to a submerged body of size r, we can expect errors of order similar to (1 + 1/r)(3), as the very upper bound. (c) 2005 Elsevier Ltd. All rights reserved.