This paper reports a determination of a sewing quality index in order to assist the industry in providing quality clothing before production. The particularity of this work lies in the fact that it encompasses various sewing quality parameters (efficiency, slippage, and puckering) into a single overall quality index. Moreover, a program was investigated, to determine the quality index, so that the manufacturer has only to enter the available data. In fact, by entering the input parameters which are blend composition, seam direction, fabric mass, stitch density, and seam thread linear density, an overall quality index will be given and the seam quality as well as the defect sources will be displayed. To reach this aim, regression models were determined to predict seam quality. In this work, 18 denim fabrics were sewn with two commercial sewing threads. Their influences, ranked according to the seam quality, were also determined. The seam efficiency was calculated by determining both the seam and the fabric's tensile strength. The seam slippage was determined by calculating the difference between the elongation at the break of the seam and the elongation at the break of the fabric. Seam puckering was determined by measuring both the fabric and seam’s thickness.