What Does 10 ATM Mean on a Watch?

The '10 ATM' marking indicates that the watch has been tested to withstand a static water pressure of 10 atmospheres, which is equivalent to the pressure at a depth of 100 meters (approximately 330 feet). ATM stands for 'atmospheres,' a unit of pressure where 1 ATM equals the air pressure at sea level. Each additional ATM represents the pressure of 10 meters of water depth. The marking is interchangeable with '10 BAR,' '100M,' and 'WR100M' — all express the same level of water resistance.

It is crucial to understand that this rating is determined under controlled laboratory conditions with the watch stationary in still water. In real-world use, dynamic forces such as the impact of diving into a pool, the pressure of a shower jet, or the acceleration of a swimming stroke can momentarily create pressures that exceed the watch's rating. This is why industry guidelines recommend a 100m rating as the minimum for swimming — it provides enough margin above the actual pressures encountered.

A 10 ATM watch is generally suitable for recreational swimming in pools and open water, snorkeling at the surface, water sports like kayaking and sailing, and everyday exposure to water including hand washing and rain. However, 10 ATM is not sufficient for scuba diving, high-board diving, or use with high-pressure water equipment. For scuba diving, look for at least 200m (20 ATM) water resistance with a screw-down crown. Always ensure your watch's crown is fully pushed in (or screwed down, if applicable) before water exposure.

The '10 ATM' marking is engraved or printed on the case back of the watch. It may appear as '10 ATM', '10 BAR', 'W.R. 10 BAR', '100M', 'WR 100M', or 'WATER RESISTANT 10 ATM'. On some watches, the water resistance rating is also printed on the dial, typically near the 6 o'clock position. Dive watches with rotating bezels often prominently display their depth rating on the dial.