Slip this Katrinkles Sock Ruler right into your sock while it is still on the needles to easily gauge when to start the toe (or the gusset/heel if you are knitting toe-up socks). With inches, centimeters, US Men/Women and Euro shoe sizes etched right on, you'll always get a perfect fit! This handy ruler can be used in a few different ways. The length of a foot can be measured by standing on it. Adult socks typically have 10% negative ease, so depending on how much negative ease you like in your sock you can either use the corresponding shoe size or add in or subtract the percentage of ease you'd like.