Smartwatch sizes: 41 or 45 mm?

The bigger case gives you a slightly larger screen and a longer battery, but it is not for every wrist (sample guide).
A 41 mm watch has about a 1.9-inch screen and sits flat on a slim wrist. A 45 mm watch shows more of each message and usually lasts a few hours longer.
Both sizes are on the demo table with spare straps, so try them on for a few minutes before you choose.