Most Branvas rings are adjustable (the band opens or closes slightly to fit the wearer), which is why many ring listings show no size selector: there's nothing to choose. The measurements shown (e.g. Top Width 7.4 mm, Shank Width 3.1 mm) describe the design's proportions, not a US/EU size.
Genuinely non-adjustable rings show their available sizes and a size chart directly on the product detail page; the size options carry over to your store, your customer picks one at checkout, and the choice comes through with the order.
Size availability varies by style and can change with restocks, so there is no single catalog-wide size range. If you need a specific size for a specific piece, send us the product link and we'll check availability for you, including sizes that have arrived but aren't reflected on the page yet.
Tip for your storefront: say "adjustable" in your description and keep the band measurements visible. It answers the sizing question up front and prevents size-related exchanges on pieces that don't have sizes.