Measure the watch case diameter across the face from 9 o’clock to 3 o’clock
Measure the case thickness from the back to the highest point of the crystal
Measure the lug-to-lug distance from the top lug to the bottom lug
Measure the lug width where the strap or bracelet attaches
Measure the strap or bracelet length if needed
Check the case shape, since round, square, and rectangular watches fit differently
Compare the measurements to your wrist size
Try the watch on if possible to confirm fit and comfort