A water resistance rating tells you the pressure a watch case withstood when it was tested, not how deep you can take it. 3, 5, 10 and 20 ATM mean 3, 5, 10 and 20 atmospheres, often printed as 30, 50, 100 and 200 metres. As a general guide, 3 ATM is for splashes and rain, 5 ATM for everyday contact with water, 10 ATM for swimming and snorkelling, and 20 ATM for more time in the water. Your watch's own instructions always come first.
What Do ATM, Bar and Metres Mean?
ATM stands for atmospheres, a unit of pressure. One atmosphere is roughly the pressure of the air around us at sea level, and it is close to one bar, which is why some makers write 5 bar where others write 5 ATM. The metres figure is the same number put another way: each atmosphere is treated as roughly ten metres of still water, so 5 ATM appears as 50 m.
This is where the confusion starts. The test is made in still conditions, on a new watch. A watch marked 30 m is not meant to go 30 metres under water. Swimming strokes, diving in, the jet of a shower and a sudden change in temperature all put more strain on a case than the number suggests. Read the rating as a level of protection, not as a depth.
3 ATM (30 m): Splashes and Rain
A 3 ATM watch is made for everyday life near water rather than in it: washing your hands, a shower of rain, a splash at the sink. It is not meant for swimming or bathing, and we would take it off before a shower. Many dress watches sit here, where a slim case and a fine strap matter more than time in the water.
Frederique Constant's Stainless Steel Classic pairs a 36 mm case with a calfskin leather strap and sapphire crystal. Armani Exchange's Rose Gold Mesh Watch brings rose gold and silver tones together on a fine mesh strap. Fossil's Stainless Steel Classic keeps to a 34 mm case with a matching bracelet, and Stroili's Gold-Tone Steel Dress Watch is a slim rectangle with stone-set indices. Each is rated 3 ATM.
5 ATM (50 m): Everyday Contact With Water
5 ATM gives more margin for daily life: washing up, rain on a long walk, a hurried hand-wash with the watch still on. Some makers consider a 5 ATM watch suitable for a short swim at the surface; others do not, so this is the rating where the instructions matter most. It is not a rating for snorkelling or diving, and a 5 ATM watch is still best taken off for the shower or the bath.
Armani Exchange's Two-Tone Stainless Steel Watch combines silver and rose gold tones on a steel bracelet. Guess's IP Rose Gold Chronograph sets crystals around the bezel of a 37 mm case. Stroili's Silver-Tone Steel Dress Watch is small and delicate at 26 mm, with a lilac dial. Gagà Milano's Stainless Steel Wristwatch is a 48 mm hand-wound piece on a leather strap, a reminder that the strap has its own limits.
- Two-Tone Stainless Steel Watch
- IP Rose Gold Chronograph
- Silver-Tone Steel Dress Watch
- Stainless Steel Wristwatch
10 ATM (100 m) and Above: Swimming and Snorkelling
From 10 ATM a watch is generally suitable for swimming, in a pool or the sea, and for snorkelling at the surface. 20 ATM (200 m) adds further margin and suits more time in and around the water. Neither number makes a watch a diving instrument on its own. A watch made for scuba diving is described as a diver's watch by its maker, and its papers explain how it should be used under water.
Fossil's Gold-Tone Dress Watch shows that a 10 ATM rating need not look sporty: a white dial, crystal hour markers and a gold-tone bracelet. Maurice Lacroix's Modern Plastic Wristwatch pairs a light 40 mm case with a rubber strap. Stroili's Purple Sports Watch is rated 100 m on a soft silicone strap. Citizen's Automatic Diver's 200m Watch, rated 20 ATM, adds a rotating bezel and luminous hands and markers.
Why Leather and Water Do Not Mix
A rating describes the case, not the strap. Leather absorbs water, and repeated soaking can darken it, stiffen it, crack it at the holes and leave it smelling of damp. Sweat does the same, more slowly. A watch on a leather strap is best kept for dry days, whatever its rating; if rain catches it, let it dry naturally, away from a radiator or direct sun. For time in the water, a steel bracelet or a rubber or silicone strap is the practical choice.
Crowns, Pushers and Seals
Water resistance depends on small rubber seals, called gaskets, at the crown, the caseback, the crystal and any pushers. A few habits help them do their work.
Keep the crown pushed fully in, or screwed down if it screws, whenever the watch is near water. Do not pull out the crown or press a chronograph pusher while the watch is wet or under water, unless its maker says you may. Rinse the watch in fresh, cool water after the sea or a chlorinated pool, then dry it with a soft cloth. Keep it away from hot water, saunas and steam, because heat and sudden changes in temperature make seals expand and contract. Perfume, sun cream and cleaning products can dry out seals over time, so put your watch on after them, not before.
After a Battery Change, Have It Checked
Seals age. They dry out, flatten and lose their grip, and a knock to the case can disturb them, so a rating describes a watch that is new and well kept, not one that stays the same for ever. Opening the caseback, which happens at every battery change, also disturbs the seal. Ask whoever changes the battery to replace the caseback gasket where needed and to pressure test the watch: a check in a machine that applies the rated pressure and shows whether the case still holds it. If your watch goes in the water often, many watchmakers suggest a check every year or so. If you ever see mist under the crystal, take the watch to a watchmaker promptly rather than waiting for it to clear.
Which Rating Do You Need?
Choose for the life the watch will lead. A dress watch you wear to work and to dinner needs nothing more than 3 ATM. A watch you rarely take off suits 5 ATM, kept away from the shower. If you swim, start at 10 ATM and choose a strap that can get wet. Whichever you choose, keep the maker's instructions that come with it: they are the final word on what your watch can do, and the place we would always begin.
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