Watch water resistance ratings explained: 30, 50, 100 and 200 m

Why 30 m does not mean 30 meters deep

The rating describes the pressure the watch withstood in a static test, in a lab, with the watch held still. Real use is different. Swimming strokes, diving into a pool, jets of water and temperature changes all create brief pressure spikes and flex the seals. Gaskets also age, dry out and shrink over the years. So the printed number is a test value with a safety margin built in, not a depth you can safely reach.

Ratings are often shown in three ways that mean the same thing: meters, bar or atmospheres, and feet. One bar is roughly the pressure of 10 m of water, so 10 bar, 10 ATM and 100 m are the same rating.

What each rating is commonly considered good for

This table follows commonly published guidance. Your watch's manual or listing comes first: some makers are more cautious than this table, and their advice is the one your warranty follows.

Look up your rating in the decoder →

Maker wording can be stricter than the number

Different brands describe the same rating differently, so read the exact words in the listing or manual. A few examples from listings we track show the range.

Tissot describes the PRX at 10 bar (100 m) as suitable for short periods of recreational swimming and showering, but no diving or snorkeling. Seiko's listing for the 100 m SRPD Seiko 5 Sports says it withstands splashes, showers and short durations of immersion. Hamilton lists the 38 mm Khaki Field Mechanical at 5 bar (50 m) and describes it as ideal for swimming and outdoor pursuits. An Orient 40 mm diver style watch rated 200 m is described as suitable for serious surface water sports, but not diving, because it is not certified as a diver's watch.

The lesson is simple: the number tells you how the case was tested, and the maker's wording tells you what they will stand behind. Our guide to whether the Tissot PRX is waterproof goes deeper on one example.

What makes a real dive watch

A watch marked DIVER'S or DIVER'S 200m is claiming compliance with ISO 6425, the international standard for diver's watches. A 200 m rating on a watch without that marking does not mean the same thing. Seiko's Prospex SRPL11 listing, for example, specifies 200 m diver's water resistance with a screw down crown and screw case back.

ISO 6425 sets minimums that go well beyond a pressure test. For details, read what is ISO 6425.

• Water resistance of at least 100 m, with an overpressure test at 125 percent of the rating.
• A unidirectional bezel or other way to preselect time, with minute marks.
• Readable in the dark at 25 cm, with a running indicator visible in the dark.
• Tests for magnetic resistance, shock resistance and salt water resistance.

Note.Dive watches are a backup timing tool. Real dives are planned and timed with a dive computer, and you should follow your training agency's guidance.

How to keep a watch water resistant

1. 1

   Screw down the crown fully before any water contact if your watch has a screw down crown.

2. 2

   Never pull out or turn the crown, or press chronograph pushers, underwater unless the maker says it is allowed.

3. 3

   Rinse the watch in fresh water after the sea or a chlorinated pool, and let it dry.

4. 4

   Avoid hot showers, hot tubs and saunas. Heat makes gaskets expand and contract and is not covered by the rating.

5. 5

   Have the water resistance tested when the watch is serviced, and after any hard knock to the crown or crystal. Gaskets wear out over time.

6. 6

   If you see fog under the crystal, stop wearing it in water and get it checked quickly to prevent rust inside.

Choosing a watch by water resistance

If you swim regularly, 100 m with a screw down crown is a sensible minimum, and a real diver's watch is better. If the watch is for the office and the occasional rain shower, 30 m or 50 m is fine. A dress watch often has lower water resistance, so treat it accordingly.

Our best dive watches under $500 and best dive watches under $1,000 list each model's rating. For field watches, which often sit at 50 m or 100 m, see best field watches.

Frequently asked questions

Is a Seiko 5 water resistant? Current Seiko 5 Sports models are listed at 100 m (10 bar). Seiko's listing for the SRPD describes it as able to withstand splashes, showers and short durations of immersion. Older Seiko 5 models are often rated 30 m or 50 m, so check the caseback.

Is a 300 m water resistant watch waterproof? No watch is fully waterproof, which is why makers use the term water resistant. A 300 m rating gives a large margin for swimming and recreational diving, provided the seals are in good condition.

Can I shower with a 100 m watch? Many makers allow it, and Tissot's PRX listing mentions showering. Hot water and soap are harder on gaskets than cold water, so many owners take watches off for hot showers anyway.

Does water resistance last forever? No. Gaskets age, so the rating only holds if the seals are maintained. Have it tested at each service.