We use a conceptual framework of sizing and fit issues to describe an extended paradigm for sizing and fit, which we call mass-customized target market sizing: that is, a sizing system based on and derived from measurement data exclusively from the people who represent an apparel firm's target market. The use of the conceptual framework provides help to expand our thinking to derive innovative solutions for sizing and fit while understanding and addressing all of the issues that must be resolved in creating a new system. Advancing technologies, especially the body scanner, are the tools that make new sizing systems possible through rapid, accurate measurement of populations and development of continuously updated measurement databases that can be sorted by multiple demographic factors. Our central argument for mass-customized target market sizing is that companies that focus on a well-defined target market, that create well designed clothing and sizing systems specifically for this market using anthropometric data, that fit the full range of body types and proportions of this market, that address issues arising from this model regarding design, production and distribution, and that communicate effectively with the market can succeed as a mass-customized business in an increasingly fragmented world. Use of population data, collected and analyzed according to firm-based and consumer-based models, can provide a powerful tool to satisfy target markets and differentiate apparel companies. Target market sizing models can also be expanded to include mass-customized apparel styling models based on the variables proposed within the conceptual framework.