Considering a certain, well-defined, fixed order range, the volume fraction is defined in terms of the first derivative of the small-angle scattering (SAS) correlation function (CF) gamma(r) in the origin gamma'(0) and the average mean chord length (d) over bar (lm). If (d) over bar (lm) is unknown beforehand, this length parameter can be estimated from the behaviour of gamma(r) in most practical cases. The method and its limits are studied for selected particle models (Boolean model, dead leaves model), for which analytic expressions for gamma(r) are known. The applicability is exemplified for experimental cases, too. (C) 2002 Elsevier Science B.V. All rights reserved.