Bar / ATM Pressure Rating — What This Mark Means
A water resistance rating expressed in bar or ATM (atmospheres) instead of meters. One bar/ATM approximately equals 10 meters of water depth in testing pressure.
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Bar and ATM are units of pressure used to rate water resistance instead of meters. One ATM (atmosphere) is the average air pressure at sea level, equal to about 1.013 bar, and each 10 meters of water depth adds roughly 1 bar of pressure. So "10 BAR" on a case back expresses the same test level as "100M."
The rating describes overpressure applied in a static laboratory test under standards such as ISO 22810, not a depth the watch is certified to visit. The practical ladder is the same as for meter ratings: 3 bar handles splashes, 5 bar rain and hand washing, 10 bar swimming, and 20 bar diving-grade construction.
Where to Find It
The rating appears on the case back near the other markings, as a number followed by "BAR" or "ATM," such as "10 BAR," "20 ATM," or "5 bar." Some brands print it on the dial as well: Casio G-Shocks characteristically show "20 BAR" on the dial or bezel.
Watches sold internationally often pair units, for example "10 BAR / 100M," and US-market pieces sometimes add feet.
Common Variations
The common ladder runs 3 BAR (30m, splash-proof), 5 BAR (50m), 10 BAR (100m, swim-ready), 20 BAR (200m, dive-grade), and 30 BAR (300m, professional divers). Unit choice is largely house style: Casio and several German brands favor bar, Seiko and most Swiss brands print meters, and ATM appears on many fashion watches.
Older European watches sometimes show "atm" in lowercase, and vintage pieces may use feet alone, such as "330FT."
Common Misconceptions
Bar and ATM are sometimes assumed to be different scales, but they differ by barely one percent (1 ATM = 1.01325 bar) and are interchangeable on watches. More importantly, the bar figure is not a safe diving depth: it carries exactly the same static-test caveats as meter ratings, including gasket aging and the effects of heat and soap.
A "3 BAR" marking in particular is often over-trusted; it permits splashes, not swimming.
What to Do Next
Multiply the bar or ATM figure by 10 for the meter equivalent, then apply the standard guidance: 5 bar for splashes only, 10 bar for swimming, 20 bar for diving. See the individual WR 50M, 100M, and 200M guides for each level's practical limits.
As with any rating, have gaskets checked periodically if the watch sees regular water exposure.
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Related Markings
A marking indicating the watch's tested water resistance depth, typically shown in meters, feet, bar, or ATM. This ratin
WR 50M / 5 Bar MarkingA water resistance rating of 50 meters (5 bar/ATM), indicating the watch can handle everyday moisture like rain and hand
WR 100M / 10 Bar MarkingA water resistance rating of 100 meters (10 bar/ATM), generally considered suitable for swimming and recreational water
WR 200M / 20 Bar MarkingA water resistance rating of 200 meters (20 bar/ATM), suitable for serious water sports and recreational scuba diving. T
Commonly Seen On
Often Confused With
- WR 100M / 10 Bar Marking
Bar and ATM figures convert to meter ratings — 10 bar corresponds to the 100m class, not a literal safe diving depth.
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Frequently asked questions
What's the difference between bar and ATM?
They're essentially the same for watch ratings. 1 ATM equals approximately 1.013 bar, making them interchangeable for practical purposes.
How do I convert bar to meters?
Multiply by 10. So 5 bar equals approximately 50M, 10 bar equals 100M, and 20 bar equals 200M.
Why do some watches use bar instead of meters?
It's largely a manufacturer preference. Japanese and European brands often use bar, while others prefer meters or feet.
Is 3 bar enough for everyday wear?
Yes, for dry conditions. 3 bar (30M) can handle accidental splashes and rain but should avoid any intentional water contact.
Does 10 bar really mean 100 meters deep?
In terms of static test pressure, yes. But in practical terms, the same cautions apply as with any water resistance rating. It's suitable for swimming, not diving.
Can bar ratings decrease over time?
The rating itself doesn't change, but the actual resistance can decrease as gaskets age and degrade. Regular testing is advisable.
What does ATM stand for on a watch?
ATM is short for 'atmosphere,' a pressure unit equal to average air pressure at sea level, about 1.013 bar. A '10 ATM' watch was tested to ten atmospheres of pressure above ambient, equivalent to roughly 100 meters of static water depth.
Sources
- ISO 22810 — Horology: water-resistant watches