Depth Rating
Depth rating is the water resistance figure printed on a watch case, given in metres or ATM. It reflects a static pressure test carried out in a lab, not the depth to which you can safely dive in real water.
At a glance
- Unit
- Metres or ATM/bar
- 1 ATM is about
- 10 metre column of water
- Test type
- Static pressure, motionless
The number on the case, 100m, 200m, or 20 ATM, does not say what most people assume. It is the result of a test in which the watch withstands a set water pressure once, while perfectly still. Swimming, diving, or a wave striking your wrist pushes the momentary pressure well past that figure.
Static test, dynamic use
Manufacturers usually express the pressure in ATM (atmospheres) or bar. One ATM is roughly the pressure of a ten metre column of water, but only in still equilibrium. You will find how that pressure is actually measured under water resistance and ATM and bar.
What the figure permits
- 30m / 50m: daily wear, hand washing, rain; swimming is not advised
- 100m: swimming and snorkelling, borderline for real diving
- 200m and above: suitable for scuba; this is the tier where genuine dive watches sit, and many, though by no means all, meet the ISO 6425 dive-watch standard
When you are choosing a real dive watch, our guide to the best dive watches under £500 is a practical starting point. For more, browse the water and diving category.
Examples
An Orient diver rated to 200m clears the static test with a comfortable margin for swimming and snorkelling, not just splashes.
View this watchA watch printed with 100m lets you swim and snorkel, but that figure is not a permit for deep scuba diving.
Comparison
The number on the case is not the same as a safe working depth.
| Option A | Option B | Notes |
|---|---|---|
| Depth rating (static) | Safe diving depth (dynamic) | The rating is a lab test at fixed pressure; in real diving, movement and water flow raise momentary pressure, so the safe depth sits below the printed figure. |
Related terms
Watches that show this
Frequently asked questions
Can I swim with a 30m water resistant watch?
No, it is not advised. A 30m rating only means protection against hand washing, rain, and light splashes. Swimming raises the momentary pressure above that static test value through arm movement, so keeping it out of the water is safest.
Why is depth rating not the real diving depth?
Because the rating is a static test where the watch holds a fixed pressure while motionless. In real diving, swimming, current, and sudden moves raise the momentary pressure on the case, so the safe working depth is always kept below the printed figure.
How do ATM and metres relate?
Roughly, 1 ATM equals the pressure of a ten metre column of water, so 20 ATM appears as 200m on the case. Both express the same static pressure in different units; neither states a real diving limit.