The numbers printed on a watch case back can be confusing. A watch marked 30 meters is not a diving watch, and the label does not mean you can safely take it that deep. Here is how to read it in real life.
What ATM Means
ATM stands for atmospheres of pressure. The rating comes from laboratory testing under still conditions, not from real movement in water, which adds extra pressure.
Typical Ratings in Everyday Use
| Rating | Good for |
|---|---|
| 3 ATM (30 m) | Rain, hand washing, light splashes |
| 5 ATM (50 m) | Showering and brief shallow water exposure |
| 10 ATM (100 m) | Swimming and water sports |
| 20 ATM (200 m) and above | Serious water activities |
Always follow the guidance from the maker of your specific watch, since ratings and use cases vary.
Tips to Protect Your Watch
- Never press buttons or pull the crown while the watch is wet.
- Rinse it with fresh water after salt water or a pool.
- Avoid hot showers and saunas, since heat can weaken the seals.
- Check the seals after a few years or after any impact.
The Bottom Line
For everyday wear, 3 to 5 ATM is plenty. If you swim often, choose a higher rating. Explore the Tomi watch collection to compare styles.