At least once a week when I ask someone what their shoe size is, I get the following answer, “It depends on whether I’m wearing tennis shoes or other shoes”. When asked to clarify, I am told the tennis shoes are always purchased a size larger than the other shoes. Translation. “I wear a size 8 in my workout shoes and a size 7 in all of my other shoes”. Does this make sense? Of course not.
The way you determine proper size should be consistent no matter what style shoe you wear. If your heel to toe measurement is an 8, then that’s your correct size. If your heel to ball measures a 7, then that’s your correct size. Your correct size should be independent of shoe design, unless of course the shoe being measured is not true to size, i.e. ‘disproportional’, in which case all bets are off.