When reviewing a watch’s specifications, the ATM rating almost always appears. Many people wonder what ATM means on a watch or what indications such as 3 ATM watch, 5 ATM, or 10 ATM actually represent. These indications are often misinterpreted because they do not indicate actual depth but rather a pressure measurement. Understanding a watch’s ATM rating is essential to know whether it is safe to swim, bathe, or simply expose the watch to water.
What does ATM mean on a watch?
ATM stands for “atmosphere,” a unit of pressure used in physics. In watchmaking, ATM indicates a watch’s water resistance. One atmosphere roughly corresponds to the air pressure at sea level.
If a watch is rated 3 ATM, 5 ATM, or 10 ATM, it means it has been tested to withstand pressure equivalent to three, five, or ten times normal atmospheric pressure. In other words, ATM measures the maximum pressure the watch can withstand in laboratory tests, not the actual depth it can reach.
ATM, meters, and water resistance: a common misconception
Ratings such as “30 m,” “50 m,” or “100 m” are based on a theoretical conversion between pressure and depth. In practice, this conversion is misleading. Water resistance tests are performed under static conditions, without movement, according to standards like ISO 22810.
In real life, a watch is subject to dynamic pressure. Wrist movements, swimming, diving, or water jets can apply pressures much higher than those simulated in tests. Therefore, a watch marked “30 m” or “3 ATM watch” is not designed to be used at 30 meters depth or for swimming.
What does 3 ATM mean on a watch?
A watch with the 3 ATM marking offers minimal protection against water. It is designed to withstand rain, handwashing, or occasional splashes.
This level of water resistance does not allow prolonged immersion. In practice, it means the watch is not suitable for water activities.
Can you swim with a 3 ATM watch? No. Even a calm swim in a pool or the sea exposes the watch to pressures and immersion times incompatible with 3 ATM.
What does 5 ATM mean on a watch?
The 5 ATM watch rating corresponds to an intermediate level of water resistance, common in everyday watches. A 5 ATM watch has been tested to withstand higher pressure than a 3 ATM watch, allowing moderate immersion.
So, what does 5 ATM mean on a watch? It means the watch can be exposed to water more regularly but not to high pressures.
Can you swim with a 5 ATM watch? Yes, under controlled conditions. Calm swimming without diving or sudden movements is generally safe. Water sports and diving are not recommended.
What does 10 ATM mean on a watch?
A 10 ATM watch is designed to withstand significantly higher pressure, offering a comfortable safety margin for common water activities.
10 ATM on a watch means it is suitable for regular aquatic use, with enough resistance to swimming movements.
Can you swim with a 10 ATM watch? Yes. It is suitable for swimming and snorkeling, as long as scuba diving is not practiced.
20 ATM, 50 ATM, and 100 ATM watches: what are they for?
From 20 ATM onwards, watches are suitable for recreational diving. These models are designed to withstand high pressure and prolonged submersion.
Watches rated 50 or 100 ATM are intended for specialized, often professional uses. They usually comply with the ISO 6425 diving watch standard and offer resistance far above the needs of most users.
Common mistakes with ATM watches
A common mistake is assuming an ATM watch is completely waterproof. In reality, no watch is fully waterproof. Heat, steam, chlorine, salt, and natural wear can reduce water resistance.
Showering with the watch, pressing buttons underwater, or neglecting water resistance checks can compromise water resistance, regardless of the ATM rating.
ATM is a key indication for understanding a watch’s water resistance. 3, 5, or 10 ATM correspond to specific usage limits. Always use the watch according to its ATM rating.
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