ATM Rating
A watch specification field known as ATM Rating, used to describe or compare a measurable or identifying characteristic of a watch.
Also known as: Atmospheres, Atmosphere rating, ATM water resistance
Definition
ATM is shorthand for atmosphere and is commonly used on watches as a pressure-based water-resistance rating. One standard atmosphere is about 1.01325 bar; in everyday watch marking, 10 ATM is commonly treated as approximately 10 bar or 100 metres of water-resistance rating. These are pressure equivalences used for rating and testing, not a guarantee that every activity at the nominal depth is appropriate.
Why it matters
ATM helps compare water-resistance specifications across brands, but activity suitability also depends on case design, condition and whether the watch meets a diving standard.