The Apple Watch Solo Loop size is effectively mapped to the holes in the Sport Loop, according to John Gruber. The distance between the holes in each Apple Watch Sport Band is reportedly exactly the same as the distance between the 12 sizes of Solo Loops on Apple’s measuring tools.
All Apple Watch Sport Bands have seven holes. For 38 mm or 40 mm tape, the S / M tape Solo Loop corresponds to the sizes of one to seven, and the M / L tape corresponds to the Solo Loop sizes from four to 10. For the 42 mm or 44 mm tape, the S / M tape is the M tape corresponds to the Solo Loop sizes of three to nine, and the M / L band corresponds to the Solo Loop sizes of six to 1
A few people have wondered why Apple does not just map fluoroelastomer Sport Band sizes to Solo Loop sizes. I can see why Apple does not – they can not assume that everyone already has access to an Apple Watch with a Sport Band, and even for people who have access to one, Apple can not assume that it is the right size (38 / 40mm versus 42 / 44mm). And to complicate matters further, each Sport Band has two sizes for the side with the holes: “S / M” and “M / L.” So there are four separate surveys from Sport Band holes for the new Solo Loop sizes.
The image below shows size mapping for two 40 mm Apple Watch Sport bands, with S / M and M / L sizes.
The following image shows size mapping for two 44mm Apple Watch Sport bands, also with S / M and M / L sizes.
The news that it is possible to match the Solo and Braided Loop size of the Sport Band will reassure many existing Apple Watch users who have been concerned about size issues and the potential need for an impractical return.
Regarding Apple’s measuring tool, Gruber points out that “I think you should use the tool to measure the circumference of your wrist accurately, not to simulate the circumference of what you think would be a comfortable watch strap,” and he believes this may be the result of much dissatisfaction with the size of the Solo Loop.