Concept of color strength is important economically and in terms of coloristical. There are various methods to determine the color strength including absorptiometry, reflection method and etc. that their results are different and not comparable. While the concept of color strength is based mainly on the visual assessment, so the results of the determination of color strength by machine methods should not contradict visual evaluations. The goals of this project are the study of the dye strength using the K/S function and principal component analysis, the scalable range as a criterion to determine and assess the strength of dye and also the study of the spectral behavior of the dye in outside of this range, which is the linear region of the K/S function against the concentration. It is expected that if the appropriate range is determined, the color strength values obtained from different methods will be comparable. In order to achieve these goals and obtain comprehensive and practical results, various samples were prepared by dyeing acrylic, polyester, wool and nylon fabrics with cationic, disperse and acidic dyes respectively. Spectral reflection data was measured and then using the principal component analysis technique the scalable range of the K/S function was determined and studied. In addition, the color properties and their effect on the dye strength were investigated. In order to confirm the results, the values of color strength (f k ) were also evaluated for dyes in this scalable range and outside of it. Finally, the results of this study showed that K/S function can be considered as the dye strength in the scalable range using the principal component analysis and plotting the changes of the K/S function in the PCA space. The results also show that the scalable range of the K/S function against the concentration can be a suitable criterion for determining and evaluating the strength of dye. Therefore, using the maximum concentration in the linear range can be cost effective in terms of energy and cost.