Abstract:The concepts of both criterion and appraisable function of size characteristics are first proposed. The size character of a material can be simply judged using the criterion, and its size distribution can be accurately appraised by use of the appraisable function. The criterion D=(a 1/a 2) ^{[1/(b 2-b 1)]}  and the appraisable function J(a, b)= lg a+b lg x are deduced from theories and have been examined with size analysis data, the results of which are satisfactory.

Key words: size size characteristics criterion appraisable function