The standard Men's width is "D". For Women, the standard width is "B". If the majority of shoes you own fit adequately, these are the widths you should select.
If the shoes you own tend to feel overly spacious in width, you should consider selecting a narrower width size. If the shoes you own tend to feel noticeably narrow or snug, then you should consider selecting a wider width size.
If your feet seem "between" sizes and you cannot decide which size to select, we suggest you choose the larger size. You can make adjustments for a better fit with socks, insoles, or a different lacing pattern.