Nike produces shoes in three size categories. They offer kids', women's and men's sizes, but these sizes are not exclusive to any age or gender. Women can still wear men's shoes, but the size they are accustomed to will be labelled differently in the men's sizes. Although the shoe size is related to the length of your foot, the sizes do not follow a direct formula. Your best bet is to consult a size conversion chart or online converter.
Find the size on a pair of well-fitting women's shoes that you own.
Subtract 2.5 from the size, if you wear a size 5 or 5.5. This will give you the equivalent men's size of 2.5 or 3, respectively.
Subtract 2 from your size, if you are a size 6. Therefore, your equivalent men's size would be a 4.
Subtract 1.5 from your size, if you are a size 6.5. This gives you the equivalent men's size of 5.
Subtract one from your size for any size 7 or greater, including half-sizes. This would give the sizes 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5 and 12 the equivalent men's sizes of 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5 and 11, respectively.