Water resistance in metres: what each figure allows
The metre figure on a watch states the static pressure it withstood in a laboratory test, not a swimming depth, so a thirty metre rating tolerates splashes only while one hundred metres permits swimming at the surface.
gelisted editorial team · Updated 15 August 2026
The short version
- A 30 metre mark equals 3 bar of static pressure in a test.
- Swimming requires at least a 100 metre rating.
- Scuba diving requires 200 metres and a screw down crown.
- Gaskets lose elasticity and should be replaced every 2 to 3 years.
The figure engraved on the case back is the most expensive misunderstanding in the sector: a 30 metre watch that goes into a swimming pool comes back with a three figure repair bill.
What the number measures
A static pressure applied in a laboratory with the watch stationary and at a constant temperature. Real water does not behave that way: a single arm stroke at the surface generates pressure peaks well above the equivalent depth, and jumping into a pool multiplies that effect. The practical scale therefore sits several steps below the engraved figure.
| Mark | Pressure | Permitted use |
|---|---|---|
| 30 m | 3 bar | splashes and rain |
| 50 m | 5 bar | quick shower, no swimming |
| 100 m | 10 bar | swimming at the surface |
| 200 m | 20 bar | scuba diving |
| 300 m | 30 bar | diving and light saturation |
| Screw down crown | recommended from 100 m | |
| Gasket replacement | every 2 to 3 years | |
| Pressure test | 20 to 50 € |
The gaskets are what fail
Water resistance does not come from the case but from 3 or 4 rubber gaskets: the crystal, the case back and the crown, plus the pushers on a chronograph. Those gaskets lose elasticity through heat, perspiration, sun creams and simple time, with a working life of 2 to 3 years. A 200 metre watch with 8 year old gaskets protects less than a 50 metre one recently serviced.
How water gets in
Operating the crown while the watch is wet, which is the most frequent cause. Failing to screw the crown back after setting the time. Using chronograph pushers underwater, which only specific models allow. And sudden temperature changes: moving from a sauna at 80 degrees into cold water creates internal condensation even in a correctly sealed watch.
If mist appears under the crystal, the watch needs a workshop within 48 hours: corrosion of the movement starts quickly and a moisture repair costs 250 € to 900 €.
The pressure test
It costs 20 € to 50 € and takes about 20 minutes in a dry or wet pressure chamber. It is worth doing annually on a watch used in the sea, and always after the case has been opened for any reason. On an island with a bathing season running from May to October, that annual expense is the cheapest insurance available for a watch of any value.
Frequently asked
+Can I swim with a 30 metre watch?
No. That rating covers splashes and rain only. Swimming needs at least 100 metres.
+What does the figure actually mean?
The static pressure withstood in a laboratory test, not a real diving depth.
+How often are gaskets replaced?
Every two to three years, since heat, perspiration and sun creams degrade them.
+What do I do if water gets in?
Take it to a workshop within 48 hours. A moisture repair costs 250 € to 900 €.
+What does a pressure test cost?
Twenty to fifty euros, taking about twenty minutes in a pressure chamber.
Sources
- 1Boletín Oficial del Estado, BOE (August 2026)
- 2Govern de les Illes Balears, Govern de les Illes Balears (August 2026)