For some models, like the Sport collection, Apple is including two bands in the box—“Small-Medium” and “Medium-Large”— while others, like the Modern Buckle straps, allow customers to pick from various strap sizes. There will be some exceptions: the gold model with Sport band is only listed as coming with one strap that “Fits 130–200mm wrists”.
The Modern Buckle bands use Small, Medium, and Large straps, while the Leather Loop, Milanese Loop, Link Bracelet, and Classic Buckle all have two different sizes for the 38mm and 42mm models. The Sport collection, as mentioned above, has Small/Medium and Medium/Large bands bundled in the box, but those vary in size for the 38mm and 42mm Sport models. So your decision might not only depend on what size face you want, but also what strap will fit you best.
Head below and click the image for the full size guide:
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Apple will also have the majority of these bands, apart from the 18k gold options, available to purchase separately ranging from $40 to $449.