Watch band size

You can match most bands with any Apple Watch Series 3 or newer case of the same size. (For Apple Watch Series 3, the 40mm band works with the 38mm case; the 44mm band works with the 42mm case.)

The Solo Loop and Braided Solo Loop bands are only compatible with Apple Watch SE and Apple Watch Series 4 or newer. Bands will only fit the selected case size and are not compatible with other case sizes. For example, a size 5 for a 40mm case does not work with a 44mm case, and vice versa.

For more info, see:

Buy Apple Watch Bands - Apple