US widths are letters. Medium is B for women and D for men.
| Width | Women | Men |
|---|---|---|
| Narrow | AA (2A) | B |
| Medium / standard | B | D |
| Wide | D | 2E (EE) |
| Extra wide | 2E | 4E |
| XX wide | 4E | 6E |
Each width step adds roughly 5 mm (about 3/16 in) at the ball of the foot, depending on length. Measure the widest part of your foot standing, in the evening. Going up half a size adds a little width but also length — a proper wide fit is better.