Understanding Watch Water Resistance: What the Numbers on Your Dial Really Mean

You've probably noticed numbers like "50m," "100m," or "10 ATM" printed on your watch dial or caseback, and assumed they tell you how deep you can swim. The reality is a little more nuanced, and misunderstanding these ratings is one of the most common ways watches get damaged. Here's what the numbers actually mean.

Water Resistance Isn't a Depth Rating

It's tempting to read "50m" as "safe to 50 meters underwater," but these ratings are based on static laboratory pressure tests, not real-world activity. Movement, water pressure changes, and temperature shifts all add stress. That's why a 50m watch is not actually meant for swimming to that depth.

What the Ratings Really Allow

• 30mmm / 3 ATM: splashes and rain only, not for swimming.

• 50m / 5 ATM: light swimming and showering, but no diving.

• 100m / 10 ATM: swimming and snorkeling are fine.

• 200m / 20 ATM and above: suitable for scuba diving and serious water sports.

ATM, Bar, and Meters Explained

These units all describe the same thing in different ways. ATM (atmospheres) and bar are nearly identical, 1 ATM is roughly equal to 10 meters of static pressure. So a watch rated 10 ATM is the same as one rated 100m. It's just a different way of printing the same specification.

Keeping Your Watch Water-Resistant

Water resistance isn't permanent. The gaskets and seals that keep water out degrade over time, especially with exposure to heat, soap, and chemicals. Never operate the crown or pushers underwater, and have your watch's seals tested periodically, particularly before a beach vacation or swim season.

At TickTock Jewelers in Burlington, vT, we offer water-resistance testing and gasket replacement to keep your timepiece protected, and we carry water-ready watches from Tissot, Seiko, Oris, and more. Before your next adventure, stop by our Bank Street showroom or call 1802.862.3042 to have your watch checked by our specialists.