A watch band should be snug enough that the watch stays put on top of your wrist, but loose enough to slide one finger underneath the band. That's the whole rule. Everything else is fine-tuning.
The one-finger test
Fasten the watch where you'd normally wear it, just behind the wrist bone. Slide a finger under the band. If it fits with light resistance, you're set. If you can't get a finger under, it's too tight. If the watch head slides around your wrist or drops over your hand, it's too loose.
Signs it's too tight
- Deep imprint of the band or caseback left on your skin after wearing.
- Pins-and-needles or visible squeezing around the band.
- Skin bulging on either side of the strap.
Signs it's too loose
- The watch face rotates to the side of your wrist during the day.
- The case slides more than an inch up and down your arm.
- The watch bangs into things because it swings on impact.
Practical notes
Wrists swell in heat and during exercise, so a band that's perfect in the morning can feel tight by afternoon; leave a little room. Metal bracelets adjust by removing links and often have micro-adjust holes in the clasp for half-steps. Leather stretches slightly with break-in, so start one hole snugger than feels ideal.
For full sizing help, see the Watch Sizing & Fit Guide and How to Measure Your Watch Strap Size.