Issue: Flat shoes: What should be the proper fit?
Solution: Your foot moves differently in flats. Flats allow your foot to fully spread out with each step. The arch is our natural, built-in spring (kind of like a built in shock absorber) and it absorbs 3-5 times our body weight with every step. To test this theory, sit down and trace your foot...then stand up and trace it. The difference is how much space you need inside your shoes.
Do the "double pinky" test!
Step #1 - When trying on flats, make sure that you can fit the tip of your pinky finger between the back of the shoe and your foot while sitting. That's how much space your toes will need to "spring forward."
Step #2 - Make sure that you can actually wiggle your toes inside the shoes. If your pinky toe is smashed, choose a bigger shoe.