"Water resistant 30 m." You've probably read it on the back of a watch and thought you could dive with it to 30 metres. You can't. Water resistance is one of the most misunderstood specs, and getting it wrong can cost you an expensive repair. Here's what each number means in practice.
Why the metres aren't real metres
The figure in metres (or ATM / bar) indicates the pressure the watch withstood in a lab test, standing still under controlled conditions. In real life, water moves, you jump, you swim, temperatures change and gaskets age. That's why the rated depth isn't the depth you can actually dive to.
What you can do at each level
- 30 m (3 ATM): handles splashes, rain and hand washing. Don't wear it in the shower or the pool.
- 50 m (5 ATM): rain, splashes and a short dip in the pool without diving in. Best to avoid frequent swimming.
- 100 m (10 ATM): swimming and surface snorkelling. This is already a watch fit for the beach and the pool.
- 200 m (20 ATM) or more: swimming, snorkelling and recreational diving. This is the standard for serious dive watches.
- 300 m, 500 m, 1000 m or more: professional dive watches, like the TAG Heuer Aquaracer 500M or the DOXA SUB 1500T. Far more than a recreational diver needs, but also a guarantee of extra toughness.
The dive watch standard
A true dive watch doesn't just have lots of metres: it meets requirements such as a unidirectional rotating bezel to track dive time, good legibility in the dark and shock resistance. The international ISO 6425 standard defines these criteria. That's why not every "100 m" watch is a dive watch.
4 rules to avoid damaging your watch
- Always keep the crown closed. If your watch has a screw-down crown, make sure it's screwed in tight before it touches water.
- Never use the pushers underwater, unless the manufacturer expressly allows it.
- Watch out for hot water: saunas, hot tubs and very hot showers make gaskets expand.
- Have the water resistance tested every one or two years, especially if you swim with your watch. Gaskets wear out over time, even if the watch looks perfect.
Our recommendation
If you want an all-round watch that goes from the beach to the office without a second thought, look for at least 100 m with a screw-down crown. And if a pre-owned watch is described as water resistant, ask when its water resistance was last tested.