Tool
Water resistance decoder
The depth on a dial is a lab test pressure, not a depth you can dive to. Pick the rating on your watch to see what it is commonly considered good for.
Short answer
A rating is a static test pressure (1 bar is about 10 m), not a usable depth. Commonly, 30 m covers splashes and rain, 50 m brief light swimming, 100 m swimming and snorkeling, and 200 m or a DIVER'S mark recreational scuba.
Decode a rating
Rating printed on the watch
100 m
10 bar static test pressure
Swimming and snorkeling. No scuba.
The number is a lab test pressure, not a usable depth: 1 bar is about 10 m of water, held still.
- Rain and splashes
- Hand washing
- Swimming
- Snorkeling
- Recreational scuba
ISO 6425 asks a dive watch for
- Water resistance of at least 100 m.
- Overpressure tested to 125 percent of the rated depth.
- A unidirectional bezel or other preselected time indicator, with minute marks.
- Readable at 25 cm in total darkness.
- A running indicator visible in the dark, such as a lume tipped seconds hand.
- Magnetic, shock and salt water resistance tests.
Always
- Seals age. Have the water resistance tested at every service, and after a crystal or caseback has been opened.
- Screw the crown down before the watch goes in water.
- Never operate the crown or pushers underwater unless the maker says the watch allows it.
- Hot showers, hot tubs and saunas are not covered by the rating: heat and steam can get past the seals.
Why 30 m does not mean 30 meters
Water resistance is tested by putting the watch under a set pressure in a still tank for a short time. Swimming, diving in and moving your arm add pressure peaks, and warm water, soap and age soften the gaskets. That gap is why commonly published guidance is much more cautious than the number on the dial.
| Rating | Test pressure | Commonly suitable for |
|---|---|---|
| 30 m | 3 bar | Splashes, rain, hand washing. No swimming. |
| 50 m | 5 bar | Brief, light swimming. No diving or snorkeling. |
| 100 m | 10 bar | Swimming and snorkeling. No scuba. |
| 200 m | 20 bar | Swimming, snorkeling, recreational scuba if it is a diver's watch. |
| 300 m and up | 30 bar and up | The same as 200 m, with more margin. |
What makes a dive watch
A watch marked DIVER'S with a depth is made to ISO 6425, which goes well beyond a pressure rating: the timing bezel, the lume, the overpressure test and the magnetic, shock and salt water tests all have to pass. The bezel turns one way only, so a knock can only make the timed dive look longer, never shorter.
More on bezels, lume and choosing a diver in dive watches.