If you have shoes that vary in size, like your running shoes versus your everyday walking shoes, then my recommendation is that you pick the size for the shoes that you wear the most. You can also pick up additional pairs today so that you don't have to hassle with changing them out every time you wear a different pair of shoes.
Below are the available sizes for WalkFit Platinum:
Mens Womens
__ 6 __ 5
__ 6½ __ 5 ½
__ 7 __ 6
__ 7½ __ 6½
__ 8 __ 7
__ 8½ __ 7½
__ 9 __ 8
__ 9½ __ 8½
__ 10 __ 9
__ 10½ __ 9½
__ 11 __ 10
__ 11½ __ 10½
__ 12 __ 11
__ 12½ __ 11½
__ 13 __ 12
__ 13½ __ 12½
__ 14
__ 14½