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.
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. Non-adjustable rings are listed in US sizing. The size guide is available on the product detail page of each non-adjustable ring.
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.