Measure around the ball of the foot. An average width woman’s size 9 foot will measure 9 inches. Multiply foot measurement times gauge, minus 10% for negative ease, for a snug foot.

9 inches x 8 stitches per inch gauge = 72 stitches x .9 = 64 stitches
or
9 inches x 7 stitches per inch gauge = 63 stitches x .9 = 56 stitches

Use a multiple of 4 stitches.