This article deals with an approach for demand modeling when designing size ranges of technical products. The proposed modeling approach is a stage of the size ranges optimization problem, and by it information can be obtained regarding the requested sizes and their respective quantities (demand). The approach is comprised of four main stagesmarket segmentation and choice of potential customers, collecting demand data, description and processing of the collected data, and determination of a demand model. The approach is applied for the demand modeling of a particular product -pneumatic modules for linear motion. In the analysis of the market research data the procedures of principle component analysis, factor analysis and regression by principal components are used. The study is carried out in the environment of STATGRAPHICS and SPSS.