In addition to adding self-measurements of feet in socks, why not add Brannock measures? I am not sure how you determine when feet size are similar, but I wear an 11.5D (with tongue cushions) and get recommendations from men in 9.5D and 10D. Yes my heel & instep girth is size 9.5 but my foot is longer and my heel to ball length is size 12 on the Brannock. No way I can wear a 10D without maiming myself. Sure my foot shape is not common but it seems that arch length is a important factor the site is leaving out.