The Apple Watch began with two simple options ... You can no longer buy the Series 3 or lower, which used 38mm and 42mm case sizes. These measurements, we should make clear, denote the size ...

Sold alongside the Series 10 ... intended for the Apple Watch Ultra. Apple's 40mm models measure in at 40mm high and 34mm wide, while the 44mm models are 44mm high and 38mm wide.