The real specs for the Apple Watch have been released:
38 mm: 136 × 170 pt @2x (272 × 340 px)
42 mm: 156 × 195 pt @2x (312 × 390 px)
In practice there's more black border. So you can still use the template – the sizing is proportional – but be aware of the new frame size. ;)
I wanted to have at hand for some mockups a template that could be as pixel-precise as possible with what we know up until now. So, here's a Sketch Template with side-by-side Apple Watch (iOS) and Moto 360 (Android Wear) that is as close as possible to the real screen.
Apple Watch (estimated)
• 42mm height × 36mm width
• ~190 × 236 pt screen
• 46mm diameter
• 320 × 290 pt screen #
Sketch template attached.
Thanks to Fabio ↬ for the support and to Matteo for the help on sizes.