Water Resistance Ratings Explained: 30m, 100m and 200m
A water resistance rating tells you what a watch can survive around water, but it is easy to read the number wrong. These figures come from a static-pressure lab test, not a depth you can safely reach. In plain terms: 30m means splashes only, 50m allows a careful swim, 100m (10 ATM) is the everyday standard for swimming and snorkelling, and 200m or more is genuinely built for the water. Here is how to read the numbers and pick sensibly.
Why the metres are not metres
The rating is measured in a lab under constant, still pressure. Real swimming adds dynamic pressure every time you push your arm through the water, and then temperature changes and ageing gaskets chip away at the margin on top. That is why a 30m watch has no business 30 metres underwater, and why you always want headroom over your intended use. You will see the figure given in metres, ATM or bar; as a rule, 1 ATM is about 1 bar is about 10 metres.
What each rating actually allows
| Rating | ATM / bar | Fine for | Not for |
|---|---|---|---|
| 30m | 3 ATM | Rain, hand-washing, splashes | Swimming, showering |
| 50m | 5 ATM | A brief swim, careful showering | Snorkelling, diving |
| 100m | 10 ATM | Swimming, snorkelling | Scuba diving |
| 200m | 20 ATM | Recreational scuba | Saturation / technical diving |
| 300m+ | 30 ATM+ | Serious and professional diving | — |
The everyday sweet spot is 100m
For a watch you never want to think about near water, 100m is the honest standard. It handles swimming, snorkelling, showers and a soaking commute with room to spare, and at that rating a watch almost always comes with a screw-down crown and better gaskets, so the whole case is more weatherproof. If you want something that copes with water and still cleans up, the best dive watches for everyday wear is a good next read, or go straight to the dive watches.
What actually keeps water out
- Gaskets: rubber seals at the crown, caseback and crystal. They harden with age, which is why resistance falls over time.
- Screw-down crown: locks the most exposed opening. Never operate it in or near water.
- Caseback: a screwed or gasketed press-fit back seals the movement from behind.
These parts tie into the wider build of the watch; the anatomy of a watch guide shows how the crown, caseback and crystal work together.
Keeping the rating alive
Water resistance is not a lifetime property. If you swim with a watch, have it pressure-tested and its gaskets checked every year or two. Keep it out of hot showers and saunas, because heat hardens seals and expands metal at different rates. Rinse it in fresh water after the sea. And a 30m dress watch stays out of the pool, full stop. Explore the full collection or more guides to match a rating to how you live.
Frequently asked questions
Can I swim with a 50m watch?
A short swim is usually fine, but 50m leaves little margin once you factor in vigorous strokes and ageing gaskets. For regular swimming, 100m is the worry-free choice.
Why can't a 30m watch go underwater?
Because the number is a static-pressure lab figure and the seals at 30m are minimal. Real swimming adds dynamic pressure the test never applies, so a 30m watch is built for rain, hand-washing and splashes only.
Does water resistance last forever?
No. Gaskets harden and shrink with age, so the rating drops over time. A pressure test and gasket check every year or two keeps a water-worn watch reliably sealed.