Watch Water Resistance Ratings Explained: 30 m to 3,900 m and What You Can Do at Each

A watch's water resistance rating is the static pressure its case withstood in a laboratory test, expressed as an equivalent depth in metres or as bar or atmospheres, and it is not a depth you can dive to. A 30 m watch should be kept out of water; a 50 m watch will survive a swim; 100 m is the practical minimum for regular swimming and snorkelling; 200 m or more, with a screw-down crown and a unidirectional bezel, is what a diver's watch carries; and the 1,220 m of a Sea-Dweller or the 3,900 m of a Deepsea are engineering margins rather than places anyone will take the watch. This guide explains what the numbers mean, how the standards behind them differ, how Rolex, Patek Philippe, Audemars Piguet and Richard Mille rate their watches, what keeps water out, why the rating fades with age, and what to check before buying a used dive watch. The Sea-Dweller collection lists the deepest-rated references we source.

Last reviewed on September 22, 2026 by Filip Biczak. Prices are dated observations, not quotes.

What do watch water resistance ratings mean?

The metre figure comes from a pressure test. A watch rated 100 m was sealed in a chamber and held at the pressure that 100 m of still water would exert, then checked for leaks. It was not lowered to 100 m, and nobody moved it while it was under pressure.

Why does 30 m not mean 30 metres of water?

Because the test is static and a swimmer is not. Moving an arm through water, hitting the surface on a dive, or aiming a shower jet at the crown briefly raises the pressure on the seals well above what the depth alone would produce. A 30 m rating gives almost no margin for that, so the manufacturers' advice for 30 m watches is to keep them dry. Temperature matters as well: a hot shower or a sauna expands the case and gaskets unevenly and can draw moisture in as the watch cools, which is why even a Submariner is better off out of the sauna. The rating is a laboratory statement about a new, sealed case; the depth you can actually use is lower and falls as the gaskets age.

ISO 22810 or ISO 6425: what makes a watch a diver's watch?

Two standards sit behind the numbers. ISO 22810 covers water-resistant watches in general and sets out a test for water resistance at the stated pressure, along with checks for condensation and for the crown and pushers under water. ISO 6425 covers diver's watches and is far stricter: it requires a minimum rating of 100 m, a device to measure elapsed time such as a unidirectional rotating bezel, legibility in the dark at 25 cm, resistance to magnetism and shock, testing at 125 percent of the rated pressure, and testing of every watch rather than a sample. A watch that meets ISO 6425 may print "Diver's" and the depth on the dial. Rolex does not print the ISO reference on its dials, but the Submariner, Sea-Dweller and Deepsea are built and tested to that standard's requirements and beyond; Rolex tests every Oyster case in pressurised water, and its dive watches are tested with an additional safety margin, as described on the Sea-Dweller page. The distinction matters when buying: a 100 m watch is water resistant, and a 300 m watch with a rotating bezel and a screw-down crown is a diver's watch, and only the latter is designed to be relied on under water.

How do Rolex, Patek Philippe, AP and Richard Mille rate their watches?

Sources: the Rolex product pages for the Submariner and Sea-Dweller lines, and the Patek Philippe Nautilus collection page. The lesson from the table is that a steel sports watch from Patek Philippe or Audemars Piguet is a swimming watch, not a diving watch, and that the Rolex professional models are in a different category from everything else on the list.

What keeps water out of a watch?

• Crown. A screw-down crown threads onto a tube in the case and compresses a gasket; the Rolex Twinlock has two sealed zones and the Triplock on the Submariner, Sea-Dweller, Deepsea and Daytona has three. A crown left unscrewed is the most common reason a water-resistant watch floods.
• Case gaskets. Rubber or synthetic rings at the caseback, the crystal and the crown tube. They compress when the watch is assembled and harden slowly over years; this is the part that ages and the reason the rating is not permanent.
• Caseback. Screw-down casebacks seal better than snap-on ones. Rolex uses a fluted screw-down back on every Oyster; Patek Philippe and Audemars Piguet use screwed sapphire display backs on their sports models.
• Crystal. Sapphire pressed into the case against a gasket. The Deepsea's crystal is 5.5 mm thick to carry the load at 3,900 m.
• Pushers. A chronograph's pushers are extra openings; the Daytona uses screw-down pushers to keep its 100 m rating, and pushers on other chronographs should not be operated under water unless the maker says otherwise.

Helium escape valves and saturation diving

Saturation divers live for days or weeks in a pressurised habitat breathing a helium and oxygen mix. Helium atoms are small enough to pass through the gaskets into the watch, and during decompression the pressure inside the case can exceed the pressure outside and blow the crystal off. The helium escape valve, which Rolex patented in 1967 for the Sea-Dweller, is a one-way valve in the case side that lets the helium out. It is relevant only to saturation diving; a recreational diver breathing air never accumulates helium, and the Submariner has no valve because it does not need one. On the wrist, the valve is a small bump on the left side of the Sea-Dweller and Deepsea cases and one of the quickest ways to tell them from a Submariner.

Does water resistance last?

No. Gaskets harden, crown tubes wear and crystals take knocks, and a rating that was accurate when the watch left the factory is only a statement of what the case can do if the seals are sound. Rolex's watch care and service page describes a full service as including replacement of the seals and a pressure test, and recommends a service roughly every ten years for current models, with a water resistance check available in between. A practical rule: have a watch pressure tested before its first swim of the season if it is more than five years from its last service, and immediately if it has taken a hard knock to the crown or crystal. A pressure test is quick and inexpensive compared with the cost of drying out a flooded calibre.

Rules for swimming with a luxury watch

• Screw the crown down every time you set the watch, and check it by hand before you get in the water.
• Rinse the watch in fresh water after the sea or the pool; salt and chlorine attack gaskets and dull steel.
• Keep it out of the shower, the hot tub and the sauna; heat and soap are harder on seals than depth.
• Do not operate the crown or pushers under water unless the maker states they are safe to use wet.
• Treat a 50 m rating as pool-only and a 30 m rating as no water at all.
• Any fogging under the crystal means water inside; stop wearing it and have the movement dried and serviced at once.
• Have a pressure test after any service, any crystal replacement and any hard knock.

Buying a used dive watch: what to check

• Pressure test result. Ask for a dated test; if there is none, price the watch as needing a seal service.
• Crown action. The crown should unscrew smoothly, set with positive clicks and screw down fully without cross-threading. A crown that will not seat means a worn tube or gasket.
• Crystal and gasket. Look for a cracked or chipped crystal edge and for a gasket visible around it; either compromises the seal.
• Caseback. Tool marks around a screw-down back show it has been opened; ask who opened it and whether the gasket was replaced.
• Dial and hands. Spotting on the dial, corroded hands or a lume plot that has lifted are signs of past water ingress, and the movement may have corroded with them.
• Bezel. Unidirectional with firm clicks and no back-play; the pip at 12 should align with the marker.
• Helium valve. On a Sea-Dweller or Deepsea, the valve should sit flush and show no corrosion.
• Price against the band. A full-set Sea-Dweller or Submariner offered well under the market is the single most reliable warning sign.

Our authentication process includes a pressure test on every dive watch before dispatch.

Quick answers

Can I swim with a 50 m water resistant watch?

Yes, in a pool, briefly, with the crown screwed down. Do not dive, shower or swim in surf with it, and treat 100 m as the sensible minimum for regular swimming.

What is the difference between water resistant and a diver's watch?

Water resistant means the case passed a static pressure test to its stated depth. A diver's watch meets ISO 6425: at least 100 m, a unidirectional timing bezel, legibility in the dark, and testing of every watch at 125 percent of the rated pressure.

Is a Rolex Submariner really good to 300 m?

Yes, when new and with sound seals. Rolex tests every Submariner case in pressurised water with a safety margin. The figure is a case rating; the practical limit depends on the gaskets being maintained.

Can I shower with a Rolex?

Better not. Heat, soap and shampoo degrade gaskets faster than cold water does, and a hot shower followed by cool air can draw moisture into the case. Rolex's dive watches will survive it; the habit shortens the life of the seals.

How often should a watch be pressure tested?

After every service, after any crystal or crown work, after a hard knock, and before serious swimming if the watch is more than about five years from its last service.

Request a Sea-Dweller or Submariner sourcing quote

Tell us the model, dial, preferred year range, condition and whether the warranty card is required, plus your budget and timing, through our sourcing enquiry form. We confirm the specific watch, photographs, card, pressure test and final price before you commit. Catalogue entries: Rolex Deepsea 136660, Sea-Dweller 4000 116600, pre-owned Sea-Dweller 116600; browse the Sea-Dweller collection, the Deepsea collection, the Submariner collection, or sell or trade your dive watch.

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