Is a "50M" watch waterproof to 50 meters?
Photo by lovstromp - CC-BY
If you just bought a watch rated “50M”, you would be forgiven for assuming that it is waterproof to a depth of 50 meters. So can you go diving with it? No way…
Ratings such as 30M, 50M, 100M and 200M indicate watches that are in some way water resistant, but are unsuitable for scuba diving. If you want to take a watch diving, you absolutely need to get one that is specifically rated for diving.
For most people a rating of 50m will be adequate for recreational swimming, and a rating of 100m will be suitable for other water sports. Here's a more detailed breakdown of what you can do with “water resistant” watches:
| 30M | 50M | 100M | 200M | |
| Perspiring | y | y | y | y |
| Car washing | y | y | y | y |
| Dishwashing | y | y | y | y |
| Walking in the rain | y | y | y | y |
| Showering | n | y | y | y |
| Bathing | n | y | y | y | Skiing | n | y | y | y |
| Parachuting | n | y | y | y |
| Swimming in still water | n | y | y | y |
| Fishing | n | y | y | y |
| Snorkeling | n | n | y | y |
| Poolside diving | n | n | y | y |
| Surfing | n | n | y | y |
| Water skiing | n | n | n | y |
| Professional water activities | n | n | n | y |
| High diving | n | n | n | y |
| Deep diving without scuba | n | n | n | y |
| Scuba diving | n | n | n | n |
Even if you follow this table, you're not supposed to press the buttons while the timepiece is wet. To maintain the water resistance you must avoid taking the watch into saunas or hot tubs, and must have the seal renewed whenever the battery is replaced.
The testing of watches for water resistance is described by ISO standard 2281. The standard only requires that a sample of watches is tested, and the sample is only tested with a static pressure (which explains why you can't actually go diving to 50 metres depth and expect a 50M watch to remain waterproof). Furthermore, not all watch manufacturers use ISO 2281.
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Watches, like the one illustrated, only claim “water resistant”, which doesn’t promise “waterproof”.
I found a watch that is advertised as “waterproof”. The specifications said “submersible 300 m”. Well, anything that sinks is submersible, but on another website it said that the crown screwed down on the case, the only way to assure waterproof.
I bought a Casio 50M watch 30 years ago. It has never left left my body other to replace the battery. I have scuba dived to 70 feet, shower, swim, sleep, work, …
I don’t understand your chart above in reference to my watch. I have finally broken the band so many times that the pin portion has broken out. I am going to buy another one.
I’m glad you have such a great watch! I’ve had a few 50M watches over the years. Some have remained waterproof in the sea while others haven’t. It may depend on how well the seal is seated when the battery is changed, as I had a couple of failures soon after a battery change.
This water resistance rating scheme is designed by the watch manufacturers themselves. Here’s Casio’s FAQ entry about water resistance ratings.
My current Casio watch is rated 100M. Interestingly, the back panel claims “Water Resistant 10 BAR”, which is the static pressure at 102 meters below sea level. Of course, dynamic pressures are much higher than static, especially in the surf.