Several basic things you already know: size (meaning length) and width (meaning across the ball of the foot). What about depth or girth – meaning from bottom to top? The depth of a shoe is often the difference between a decent fit and a great fit. Certain shoes have been designed to provide more depth than is usually provided. They often have multiple liners built in that allow you to adjust the depth even further.
Another characteristic to look for is the difference between the two types of lace shoes – bal and blucher. “Bals” are stitched across the bottom of the instep (top of the foot) and the two sides are held very close together; however, “bluchers” are designed with a “butterfly” style opening and allow the shoe to open both wider and deeper.
Years ago, there was a standard U.S. “last” and a person shopping for shoes could be measured for both length and width with confidence. Unfortunately, this time has passed. Today, every shoe manufacturer in the world uses their own last and, in most cases, they use several different lasts. Because of this, size measuring devices work only moderately well in determining length and not at all in determining width. Knowing the differences between certain lasts can be vital in fitting shoes.
There is no longer any “standard” width designation that can be counted on. For example, what Florsheim marks as a W fits exactly the same as the styles Florsheim marks 3E, while Hush Puppies W (for men) is actually an E width and their XW is the 3E.
Whenever you attempt to fit an orthotic or arch-support into a shoe, the most important thing to look for is whether or not the style has a removable liner. Without a removable liner, the likelihood of the style being able to accommodate a custom or after-market inserts is very low.
When attempting to fit a foot with any type of deformity (bunion, hammer toes, etc?) it is always best to select a style with as few seams ass possible. A plain-toed shoe will mold itself to the foot much easier and if a seam hits the foot in the wrong place it can cause serious irritation.