Measure with a tape or string:
Go around your wrist with the tape/thread and mark where the tape/thread overlaps.
Unroll your ribbon/ string, cut at the mark and then measure the length between the two ends with a ruler.
When measuring, consider how you want to wear the watch (tight bracelet or loose bracelet).
Measuring with a tape measure:
Measure your wrist circumference at the point where you usually wear your watch.
When measuring, consider how you want to wear the watch (tight or loose).