ATM-M water resistance

ATM-M Water Resistance of Watches

Water resistance of watches refers to the ability of the watch case to withstand moisture and water exposure. It is measured in meters (m), atmospheres (ATM), or bars (bar), where 1 ATM = 10 meters of water pressure = 1 bar.

Basic water resistance ratings for watches:

• Water Resistant (no number) – Resistant only to humidity and dust, not water. Not suitable for water contact.
• 30 m / 3 ATM – Resistant to rain and splashes, not suitable for swimming.
• 50 m / 5 ATM – Resistant to rain, hand washing, and showering, not suitable for swimming.
• 100 m / 10 ATM – Suitable for swimming and snorkeling, not suitable for diving.
• 200 m / 20 ATM – Suitable for recreational diving without breathing equipment.
• 300 m / 30 ATM and above – Professional diving watches, suitable for deep-sea dives.

Key aspects of water resistance:

• Laboratory values – Testing is conducted in still water under controlled conditions. Actual water resistance in real-world use is lower.
• Crown and seals – The most common entry point for water. The crown should be fully closed when in contact with water.
• Material aging – Rubber seals wear out over time, reducing water resistance. Regular maintenance is recommended.
• ISO standards – Some manufacturers use proprietary water resistance ratings, which may differ from standard norms.

Choosing the right watch for water resistance depends on its intended use. For everyday wear, models with 50 m resistance are sufficient, while for swimming, at least 100 m is recommended, and for diving, 200 m or more.