Use this as a guide. Preference is a huge factor — the benefit of a non-wire is they're super flexible, so you will likely fit in more than one size. Like a looser band? Size up! Like less coverage? Size down! Still unsure? Try two sizes :)
*Note, our Sieve Non-Wire doesn't have the same wide band as our Silky. As a result, it'll likely feel snug the first few wears. Don't fret — it'll stretch a bit with time.