Knitting fabric, which is soft, elastic and absorbent, is used widely in textile. However, this type of fabric has a week point that is dimensional instability. There are many technological parameters to affect the fabric quality such as machine gauge, yarn type, stitch density and especially the compactness factor. In this research, the authors investigated to determine the usable compactness factor on two groups of cotton Single fabric with yarn count of Ne30 and Ne36 respectively, both of them were knitted with seven levels of compactness factor 18, 19, 20, 21, 22, 23, 24 and then were laundered and dried 10 cycles. Four dimensional parameters K[1-4] were calculated after each laundering and drying cycle. With the evidence of 95 percent, the result shows that for cotton Ne30 Single fabric, compactness factor should be from 18 to 24 and the optimum value is 20
for cotton Ne36 Single fabric, compactness factor should be from 20 to 24 and the optimum value is 21.