What is 5 ATM Water Resistance? Watches’ Depth Ratings Explained

What is 5 ATM Water Resistance? Watches’ Depth Ratings Explained

Watches differ widely not only in their designs, materials, and functions but also in their ability to resist the detrimental effects of water and moisture. Some watch enthusiasts, especially those who wear their timepieces for diving, know exactly what they're looking for in terms of waterproofing, but many others might be unsure exactly how safe it is to wear their watch in the swimming pool or even to wash the car. What do watches' water-resistance ratings mean in the real world, and how exactly do industry terms like "bars" and "atmospheres" help you determine how waterproof your watch is? Here we address some commonly asked questions about water resistance in watches and break down what the most common depth ratings mean in practical terms. 

What was the first water-resistant watch?

Rolex Oyster 1926

Since the invention of the wristwatch, watchmakers have been coming up with solutions to address an inconvenient reality: namely, that water and tiny mechanical parts, such as those inside a watch movement, simply do not mix. The technical challenge of making a portable timepiece that could withstand exposure to water became even more prominent in the mid-20th Century, with the rise of diving as a tactical and eventually also a recreational pursuit. The first innovator to seriously take up the gauntlet was Rolex founder Hans Wilsdorf, who developed the now-famous Oyster case in 1926. Its groundbreaking design combined a threaded, hermetically sealed caseback and a crown that screwed securely into the side of the case for a water resistance never before achieved in watches. Debuting in a watch (above) with the same name, in the same year, the Oyster took its name from the bivalve mollusk whose traits it emulated, except that its function was the opposite, with the two “shells” of the case clamping tight to keep water outside, rather than inside. The Oyster case — which reached its pinnacle of robust waterproofness on the Submariner, Rolex’s first purpose-built divers’ watch, introduced in 1953 — has become standard in nearly all of Rolex’s sport-luxury watches today. The original Submariner was water-resistant to a then-record 100 meters, and its modern descendants have since tripled that rating. 

How long have dive watches been around?

Omega Seamaster 1948 Ad

After Rolex revolutionized watchmaking with the Oyster, other watchmakers, courting the burgeoning market for divers — military and eventually also civilian — followed suit. Florence’s Guido Panerai used Rolex Oyster cases for the original Radiomir dive watches, issued to Italian naval divers as early as 1936. Omega, one of Rolex’s major competitors, introduced its own waterproof innovation in the original Seamaster watch of 1948: a design centered around the use of a rubber O-ring gasket, of the type used in submarines, to seal the crown and case against leaks; this type of gasket proved to be more reliable than the shellac and lead versions that watchmakers had been using at the time, and set the Seamaster, originally positioned as a dress watch, on its path to becoming the full-fledged divers’ watch that it is today. The Blancpain Fifty Fathoms, introduced almost simultaneously with the Rolex Submariner and designed with the input of French military divers, established a new level of waterproofness as well as the ubiquitous dive-scale bezel that defines a “true” dive watch today. Breitling’s first Superocean in 1957 upped the ante to 200 meters, and the entire watch industry eventually joined the ongoing quest to push the frontiers of water resistance for timepieces. Rolex and Omega, in particular, have made setting underwater records part of their brands’ mission statements; their fierce historical rivalry is detailed here. Nearly every watch brand now makes at least one model aimed at divers and those looking to emulate their style.

Why do dive watches have those turning bezels, and why do they only rotate one way?

Blancpain Fifty Fathoms bezel
A groundbreaking and utilitarian element pioneered by the original Blancpain Fifty Fathoms (modern version featured above), this type of bezel is now a ubiquitous element of watches intended for underwater use. The so-called “divers’ bezel” is lockable, rotates in only one direction (counterclockwise), and is inscribed with a 60-minute scale for the purposes of setting dive times. Many dive-scale bezels have their first 15- or 20-minute sector highlighted because most timed dives will fall within this range. Coinciding roughly with the rise in popularity of scuba diving in the wake of Jacques Cousteau and Emile Gagnan’s invention of the Aqua-Lung, It was also a potentially life-saving invention: its unidirectional design prevented a diver from accidentally jarring the bezel in the wrong direction for an inaccurate reading of how much time he’d spent underwater, and thus miscalculating how much oxygen he had left in the tank. The edges of divers’ bezels, most of which ratchet with a series of 60 individual clicks for precise setting of the dive interval, tend to be designed for easy gripping by a diver wearing thick gloves.

What does “ATM” mean on a watch dial or caseback?

Doxa SUB 300 caseback“ATM” is the abbreviation for “atmospheres,” a term used to describe the level of water pressure that a watch has been tested to withstand. One atmosphere (also denoted on some watches as one “bar”) is equivalent to 10 meters of pressure; thus, a watch with 3 ATM, either engraved on the caseback (above) or printed on the dial, means it’s been tested to 30 meters worth of water pressure, 5 ATM means 50 meters of pressure, and so on. Many watch dials, perhaps as a concession to American consumers who don’t use the metric system, have the measurement in both meters and feet: 100 meters, for example, equals approximately 330 feet. Quite simply, the larger the number before “ATM,” the more water-resistant your watch will be. Dressier watches tend to be less water resistant (3 ATM or 5 ATM), while sportier, more tool-oriented models, are almost always much more robust in this area (10 ATM, 20 ATM, or even higher). The hybrid “Sport Luxury” category will offer a range of water resistance levels but usually will err on the side of a higher ATM. 

How waterproof is my watch, exactly? Can I wear it to go swimming?

As a rule, most watches nowadays are built to be water-resistant enough to handle life’s everyday encounters with moisture, i.e., rain, perspiration, an unexpected splash from a lawn sprinkler or an inconsiderate motorist plowing through a puddle. But the level of water resistance indicated on the watch’s dial (via ATM, meters, and/or feet) should be heeded as an indicator of what it can reasonably be expected to withstand.

3 ATM/30 meters: This is generally the lowest level at which a watch can be called “water resistant” enough for everyday wear. It can withstand accidental splashes but shouldn’t be worn for activities in which it will encounter more water than that, like bathing, showering, or swimming. Appropriately, this low rating is reserved for watches that you probably wouldn’t want to get wet anyway, like the ones you’d wear for an elegant night out or a formal occasion like a wedding.

A. Lange & Söhne Lange 1

Examples: Bulova Sutton, Junghans Max Bill Chronoscope, Grand Seiko Elegance Mechanical, A. Lange & Söhne Lange 1 (pictured), Patek Philippe Calatrava

5 ATM/50 meters: The norm for many dress watches, this is the water-resistance level where you don’t have to fret about wearing your watch in the shower or bathtub — or while washing dishes or hosing down the car — but you still wouldn’t want to leave it on while you’re going for a swim (and certainly not for an extended period underwater, such as a dive). 

Raymond Weil Millesime Small Seconds

Examples: Frederique Constant Highlife Automatic, Raymond Weil Millesime (pictured), MeisterSinger Lunascope, Glashütte Original Senator Excellence, Audemars Piguet Royal Oak

10 ATM/100 meters: Once the gold standard of water resistance after it was achieved by the original Rolex Submariner and others in the 1950s, 100 meters is now considered fairly pedestrian for watches intended to be worn underwater. As per the ISO 6425 international standard for what constitutes a “diving watch,” a depth rating of 100 meters (10 ATM) is the minimum requirement for the category. Most purpose-built dive watches have higher depth ratings these days, but the 100-meter baseline is still regarded by many as the benchmark for any watch considered “Sport.” If your watch touts this level of water resistance, you can feel comfortable wearing it for a swim or even for light diving or snorkeling.

Tissot PRX Powermatic 80

Examples: Longines Conquest, Tissot PRX Powermatic 80 (pictured), Hamilton Khaki Field Murph, Chopard Alpine Eagle, Zenith Chronomaster Sport

20 ATM/200 meters: The modern baseline for a watch intended for serious scuba diving (rather than just swimming). Many popular dive watches feature this depth rating, which of course also indicates a watch that can go deeper underwater than any actual human diver. If your watch's dial or caseback reads “20 ATM” and/or “200 meters,” and if its 60-minute bezel turns in one direction and its crown screws into the case, you can rest assured you’ve got a solid dive watch on your wrist that you can put through its underwater paces. 

Citizen Promaster Dive Automatic

Examples: Citizen Promaster Diver (pictured), Seiko Prospex “Arnie,” Tissot Seastar, Zodiac Super Sea Wolf, Tudor Black Bay Fifty-Eight

30 ATM/300 meters: This is the level at which the big boys of the genre play. Omega’s first Seamaster Professional 300 model, released in 1957, claimed to be the first watch that offered this elite level of waterproofness, even though testing equipment at the time could only confirm it to 200 meters. Doxa introduced its first SUB 300 model in 1967, and Rolex released the first Submariners with 300-meter Oyster cases in 1987. A 300-meter dive watch, like the models listed below, is one that can be worn both for watch-enthusiast bragging rights as well as actual diving.

Omega Seamaster Diver 300

Examples: Doxa SUB 300, Omega Seamaster Diver 300M (pictured), Rolex Oyster Perpetual Submariner, Breitling Superocean Automatic 42, TAG Heuer Aquaracer Professional 300, Rado Captain Cook Automatic

50 - 100 ATM/500 - 1,000 meters: At this level of water resistance, we’re beyond the usual parameters of everyday wear, and even recreational diving, and into the realm of saturation diving  — i.e., divers plying their trade at great depths, inside a pressurized diving bell, breathing a mixture of hydrogen, helium, and oxygen to sustain them for prolonged periods underwater. Accordingly, many of these “extreme” dive watches also incorporate a built-in helium release valve in the case (a device pioneered by Rolex with its original Sea-Dweller model in 1967), which automatically releases built-up helium atoms that could otherwise penetrate the watch and cause its crystal to pop free. Whereas the Submariner, Fifty Fathoms, and Seamaster remain favorites among watch enthusiasts and collectors, whether or not they’re ever worn for diving, rocking one of these watches — which are usually very large and very thick and rarely designed with luxury in mind — tends to establish you as a member of a rather select fraternity of hardcore diving enthusiasts. 

Oris ProDiver

Examples: Rolex Sea-Dweller, Bremont Supermarine S500, Seiko Marinemaster Professional, Oris AquisPro (pictured), TAG Heuer Aquaracer Professional 1000 Superdiver

What is the most water-resistant watch today?

Rolex Deepsea Titanium

With the popularity of dive watches and diving-inspired watches continuing unabated for the past several decades, along with advances in watchmaking technology, you can now find watches on the most extreme end of water resistance, although such timepieces are, understandably, still niche items in the overall watch market. Examples include the Doxa SUB 1500T (water resistant to 1,500 meters),  Sinn U2 EZM 5 (2,000 meters), Zelos Abyss 3 (3,000 meters), and Rolex Deepsea Sea-Dweller (3,900 meters). Perhaps inevitably, it is Rolex and Omega that have most notably vied for the title of most waterproof watch in the 21st Century. In 2012, Rolex made a special Deepsea Sea-Dweller prototype used by movie director James Cameron for his record-setting submarine expedition that descended 35,787 feet, or 10,907 meters, below the surface in the Pacific Ocean’s Mariana Trench. In 2019, Omega responded with its own prototype, the Seamaster Planet Ocean Ultra Deep, used by explorer Victor Vescovo to descend even deeper into the Mariana Trench, to 35,853 feet, or 10,927 meters. The commercial version of the Ultra Deep, released shortly thereafter, boasted a water resistance of 6,000 meters, at the time the highest level available in a watch you could actually buy and wear. Rolex upped the ante yet again in 2023 with the newest version of the Deepsea Challenge (above), with a hulking 50mm case (more than 20mm thick) made of light-but-robust RLX titanium and water-resistant to a new-record depth of 11,000 meters (35,800 feet). Whichever watchmaker takes the prize for the next record, one things seems certain: wristwatches will continue to explore new heights of technology in order to achieve new depths in water resistance. 

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