As markets fragmented into a plethora of submarkets, coping with various customers demands is becoming time consuming and expensive. Recently software product line (SPL) approach has shown many benefits as opposed to single product development approach in terms of quality, time-to-market, and cost. However, quantitative market-driven scoping method from existing or future product portfolio and relating customers to products has not been explored. Even though setting the proper scope of the product line is the first step to establishing initiatives in software product line, a market-driven scoping based on engineering principles has not been fully exploited. In this paper, we propose a market-driven quantitative scoping method. This method incorporates customers' needs, product family structure and market strategies into scoping such that this ensures that SPL derivatives penetrate market grids.