What does 100 m (10 bar) water resistance really mean?

What does 100 m (10 bar) water resistance really mean?

10 bar water resistance, also written 100 m or 10 ATM, is a pressure rating from a controlled test, not a depth. Here is what the ratings mean, what makers say each one suits, and what wears them down.

10 bar water resistance, also written 100 m or 10 ATM, is a pressure rating from a controlled test, roughly the pressure of 100 metres of still water. It is not a measure of how deep a watch can go, and makers disagree about what each rating suits. A water resistant watch resists water up to a stated pressure.

This page explains what the ratings mean, sets out what several makers say each one suits, shows where they disagree and lists what wears the rating down. Vannin's first watch, the Field Watch, is listed at 100 metres / 10 ATM and is coming soon, so we have an interest. The explanation rests on standards bodies and other makers' own pages.

What does 10 bar water resistance mean on a watch?

10 bar water resistance means the case is rated for a static test pressure of about 10 bar, roughly what 100 metres of still water exerts. Makers write it as 100 m, 10 bar or 10 ATM. Water resistant 10 bar, 10 bar water resistant and water resistance 10 ATM all describe the same kind of rating, and none of them is a promise about the sea.

The Federation of the Swiss Watch Industry (FH) says the rating is shown in bar or metres on the watch or in its papers, and puts 2 bar at about 20 metres. That makes 1 bar about 10 metres, which is our arithmetic. We write "about" throughout, because no metrology source we could reach gives an exact conversion.

• FH

100 m, 10 bar and 10 ATM: one rating, three labels

One bar is about the pressure at 10 metres of water, and one atmosphere is about one bar. Citizen says the same in its support pages. So 100 m, 10 bar and 10 ATM are three labels for roughly the same rating, and 100 m is about 330 ft (Oris writes 328 ft). In the same way, 5 bar is about 50 m and 20 bar about 200 m.

• Citizen

What a water resistant watch means

A water resistant watch is designed to keep water out up to a stated pressure under stated conditions. ISO 22810:2010, the standard for water-resistant watches, sets a minimum test of 2 bar, about 20 m, and lets a maker add bar or metre figures if the watch was tested higher, according to World Tempus. Water resistant watches keep that rating only while their seals stay in good order, so it is a design limit and not a permanent property.

• World Tempus

Why 100 m is a test pressure, not a diving depth

The number comes from a test in which the water, the watch and the temperature are held still, so it states the steady pressure the case is rated for, not how deep a person can go with it. Aquastar, a dive-watch maker, describes the rating as a static laboratory result.

Swimming, diving and quick arm movements add short pressure spikes, Aquastar says, which is why it calls the printed figure a margin of safety rather than an operating limit. Longines says its figures show the static pressure a watch can withstand, not the depth it can be immersed to. We give no number for the extra pressure, because the sources we read give none.

That is why the same number can mislead. Reading "100 m" as a permitted depth treats a laboratory figure as an operating limit. Casio's manuals and Citizen's support pages describe each marking in terms of activities, not depths, and FH says a watch's water resistance is also set by the model's specification, so you should follow the maker's instructions for use and care.

ISO 22810 leaves it to the maker to state which activities a watch suits, according to the preview pages of the standard that we read. That is one reason advice differs from brand to brand, and why the next section sets it side by side.

A 100 m watch is therefore not a 100 m dive watch. Divers' watches follow a separate standard, which the section on ISO 22810 and ISO 6425 below sets out.

• Aquastar

Watch water resistance chart: 30 m, 50 m, 100 m, 200 m and dive ratings

At 30 m, makers describe rain and splashes. At 50 m they disagree about swimming. At 100 m the makers we checked say swimming is fine and several add snorkelling. At 200 m the advice widens, and only a watch marked "Diver's" is covered by the dive standard. This chart summarises makers' pages. It is not a standard.

What does 5 ATM water resistant mean? It is the 50 m row, and a 200m water resistant watch is the 200 m row. Swimming is where advice for a 50m water resistant watch divides, as Table 2 shows.

Yes: every maker checked that addresses it says yes. No: every maker that addresses it says no. Mixed: makers disagree (see Table 2). Not listed: none of the makers checked addresses it, so this page says nothing either way. Showering is the thinnest column, so those cells name Seiko, the only maker whose page lists it. Casio's website guides could not be read when we checked, so the Casio rows rest on two operating manuals.

Where makers disagree

The same rating gets different advice from different makers, and sometimes from different pages of one maker. Table 2 shows each maker at 100 m / 10 bar and at the ratings either side.

Oris says watches below 10 bar must not be worn in water, while Casio, Citizen, Longines, Orient, Seiko and Timex all describe swimming at 50 m. Casio's tables allow hand washing, yet the same manuals advise against wearing the watch while washing with soap. Seiko's UK page words 10 bar differently from its global page. The conflicts are real, so we show them rather than rank the makers.

Aquastar, whose pages we use for other points, gives a similar ladder: splashes at 30 m, careful pool swimming at 50 m, and swimming and snorkelling at 100 m, which it calls the practical floor for confident use in water. It sits outside the tables because it is one dive-watch maker's guidance, not a general chart.

Showering: makers say little and disagree. Seiko groups it with swimming from 5 bar, and FH says a watch described as water-resistant can be worn while showering. Casio's manuals advise against wearing a watch in a bath, a heated pool or a sauna. Ask your watch's own manual.

Aquastar: what does water resistance rating mean; Casio: operating precautions, module 3569; Casio: operating precautions, module 5710; Citizen: precautions for calibre E81; Citizen: precautions for calibre H29; Citizen: precautions for calibre H80; Longines: water resistant watches blog (UK); Orient USA: what water resistance really means; Oris Help Centre: how water-resistant is my watch; Rolex: Oyster Perpetual user guide; Seiko Watch Corporation: water resistance FAQ (global); Seiko Watch Corporation: water resistance FAQ (UK); Timex: water resistance ratings; Timex: what makes a watch water resistant (blog)

• Casio (operating manuals)
• Citizen (support guides)
• Longines (water resistant watches blog)
• Orient (USA blog, January 2017)
• Oris (Help Centre)
• Seiko (Water Resistance FAQ)
• Timex (Water Resistance Ratings)
• Aquastar: what does water resistance rating mean
• Casio: operating precautions, module 3569
• Casio: operating precautions, module 5710
• Citizen: precautions for calibre E81
• Citizen: precautions for calibre H29
• Citizen: precautions for calibre H80
• Longines: water resistant watches blog (UK)
• Orient USA: what water resistance really means
• Oris Help Centre: how water-resistant is my watch
• Rolex: Oyster Perpetual user guide
• Seiko Watch Corporation: water resistance FAQ (global)
• Seiko Watch Corporation: water resistance FAQ (UK)
• Timex: water resistance ratings
• Timex: what makes a watch water resistant (blog)

Is a 100 m water resistant watch safe for swimming?

Several makers say yes to swimming at 100 m / 10 bar: Casio, Longines, Seiko and Timex, and Oris says watches rated 10 bar or more may be worn in water. Each speaks only for its own watches in good condition, and none reads 100 m as a depth the wearer can reach. US sites call it a "100 meter water resistant watch"; the rating is the same.

Whether a particular watch is safe for swimming depends on several things the makers name:

Seals in good condition. Oris, Seiko and Aquastar all say seals age, and Casio says to replace gaskets periodically. A crown and pushers that are fully closed and never worked while wet. Casio, Oris, Orient, Rolex, Seiko and Timex say so. No soap, heat or steam. Casio's manuals advise against wearing a watch in a heated pool or a sauna or while washing with soap, and Timex lists soap among the things that can damage a watch. No recent hard knock. Oris and Seiko both say a shock can affect the seal.

The wording about diving varies more than the wording about swimming. Casio's manuals, Citizen, Orient and Seiko say a watch at this rating may be used for skin diving, while Longines and Timex name snorkelling. Skin diving is the term Casio, Citizen and Seiko use for diving without an air tank, while scuba diving uses air tanks and saturation diving uses helium gas mixtures, in Citizen's wording.

At this rating, Casio, Citizen, Longines and Seiko do not recommend scuba. Orient reserves scuba for watches that meet ISO 6425, and Timex's ratings page lists scuba from 200 m. Your watch's own manual outranks any chart, including ours.

Water resistant vs waterproof watch: are watches waterproof?

No. "Waterproof" suggests protection that never fails, which no watch seal can offer, so the standards and most makers say "water resistant". A watch described as water resistant is built to resist water up to a stated pressure, and that stated limit matters more than the word.

There is some US history here. The Federal Trade Commission's Guides for the Watch Industry advised against calling a watch waterproof, and commenters told the FTC that "proof" implies absolute protection. The FTC rescinded the Guides effective 9 June 1999, saying international standards give enough guidance and that its general deception law still applies, in its rescission notice. That is history, not a current rule: the Guides no longer exist.

Industry commenters gave their reasons. A Swiss industry comment recorded in the FTC's notice says "proof" implies a measure of absolute protection that does not exist for watches, especially over long periods, and Timex told the FTC it knew of no watch on which immersion would have no effect at any depth or duration. Timex's ratings page defines waterproof as letting no water pass through.

Usage is not uniform. Timex says it sells only water-resistant watches, and the Aquastar and Seiko pages we read use "water resistance". Rolex's Oyster Perpetual user guide says "waterproof" throughout. The ISO titles say "water-resistant" and "divers'". The number and the maker's guidance matter more than the word.

UK searchers often ask about a waterproof watch, and the honest answer is the same: read the stated rating and the maker's guidance, and treat neither as a guarantee. A rating also describes a watch in good condition and wears down, as the limits section below explains.

• rescission notice

ISO 22810 and ISO 6425: the standards behind the marking

Two ISO standards sit behind the markings: ISO 22810:2010 for water-resistant watches and ISO 6425:2018 for divers' watches. A 100 m marking on a watch that is not marked "Diver's" falls under the first, where the maker chooses its own tests, and not under the dive standard.

FH says a watch that its maker describes as water-resistant or as a diving model must comply with international standards. It describes a diving watch as a water-resistant watch that also meets extra standardised criteria, including water resistance of at least 100 metres (10 bar). BSI carries ISO 22810 in its catalogue and notes that divers' watches, specified as such, fall under ISO 6425.

We read the ISO catalogue pages, a preview extract of ISO 22810 and secondary descriptions. We have not read the full text of either standard, so this page gives no test durations or temperatures.

Three points follow from Table 3. A 100 m marking on a watch not marked "Diver's" is set by that maker's own test, and under ISO 22810 the maker chooses its tests and sampling. The maker also decides which activities are covered and what care precautions apply, according to the preview extract. And only "Diver's" watches carry the extra requirements and the 125 per cent test.

ISO lists ISO 22810:2010 as confirmed in 2021, with a systematic review opened in 2026 and no outcome shown when we looked, so we name the year and do not call it final. The same sources are linked here: FH, the ISO 22810 catalogue page and the ISO 6425 catalogue page.

Aquastar: what is ISO 6425; BSI Knowledge: Horology, water-resistant watches; FH: a reality check on watches' water resistance; FTC: Guides for the Watch Industry, 16 CFR Part 245 (rescission, 1999); ISO 22810:2010 catalogue page; ISO 22810:2010 preview extract (ANSI webstore); ISO 6425:2018 catalogue page; Time Transformed: diving watches and ISO 6425; World Tempus: publication of standard ISO 22810

• FH
• ISO 22810 catalogue page
• ISO 6425 catalogue page
• Aquastar: what is ISO 6425
• BSI Knowledge: Horology, water-resistant watches
• FH: a reality check on watches' water resistance
• FTC: Guides for the Watch Industry, 16 CFR Part 245 (rescission, 1999)
• ISO 22810:2010 catalogue page
• ISO 22810:2010 preview extract (ANSI webstore)
• ISO 6425:2018 catalogue page
• Time Transformed: diving watches and ISO 6425
• World Tempus: publication of standard ISO 22810

What wears down water resistance (and why makers say to have it tested)

Water resistance depends on seals that age, so several makers say to have the case checked at set intervals: the factory test only shows the watch as it was on the day. Table 4 lists seven things makers say wear it down. A leather strap is a strap issue and not a case-seal issue.

The crystal is a separate part of the case, and we cover it in sapphire crystal versus mineral glass. This page does not describe any watch's seals.

• sapphire crystal versus mineral glass

How often should water resistance be tested?

Intervals differ by maker. Aquastar says to inspect gaskets and pressure test roughly every couple of years for a watch used in water. Casio's manuals say to replace gaskets about every two or three years, and Oris says to have the water resistance checked annually through an authorised dealer, because the factory test is a snapshot. Rolex and Seiko say periodically, with no figure.

Servicing is the other route. Rolex says a full service ends with tests that include the case's resistance to water, Seiko recommends a periodic overhaul to check water resistance, and Casio says a trained technician inspects water resistance whenever the battery of a battery-powered watch is replaced.

A pressure test is a professional check of the case seals, not something to attempt at home. Follow the interval your own watch's maker gives.

What a 100 m rating does not guarantee

A 100 m rating guarantees nothing beyond what the maker states for that watch, in good condition. It does not mean:

A depth. It is a test pressure, set under static laboratory conditions. A watch in any state. The rating describes a watch as it was when tested, and ISO's own preview says protection depends on construction, manufacturing quality and the watch's history, such as service and shocks. The same thing from every brand. Under ISO 22810 the maker sets its tests and decides which activities are covered, so "100 m" compares across brands only loosely, as Table 2 shows. A dive rating. Legibility in darkness, an elapsed-time device and the shock, magnetism, salt-water and strap tests belong to ISO 6425 and "Diver's" watches. This page does not say what ISO 22810 leaves out. Cover for heat, steam, soap, knocks, an open crown or a leather strap. Permission. The charts here, ours included, are summaries, and FH advises following the maker's instructions for use and maintenance.

None of this makes a 100 m rating meaningless. It tells you the case was rated for a stated test pressure, which is a useful starting point. What a given watch suits is the maker's call, and what it can still do depends on its condition.

A worked example: 100 m / 10 ATM on the Vannin Field Watch

The Vannin Field Watch is coming soon and is listed at 100 metres / 10 ATM. The Field Watch pages carry that same figure, and it is the only one this page uses. Everything above applies to reading that number: a pressure rating of about 10 bar, not a depth. If the term is new to you, what a field watch is explains it.

In the tables above, the 100 m band is where several makers describe swimming and some add snorkelling. That is what those makers say about their own watches, according to their published pages. We make no claim about any activity in water beyond the stated rating.

The listing gives a rating only, and it does not make the Field Watch a dive watch. A dive watch collection in development is a separate project, and we have no specifications or dates to share. Visitors can register their interest on the Field Watch pages.

As with any watch, follow the care guidance for your specific watch. Vannin's current care guidance is on the watch care page.

• Vannin Field Watch
• what a field watch is
• A dive watch collection in development
• watch care page

Frequently asked questions

What does water resistant mean for a watch? It means the case is designed to keep water out up to a stated pressure under stated conditions. ISO 22810 sets a minimum test of 2 bar, about 20 m, and the maker decides which activities a rating suits. It is not permanent, because seals age. The chart above shows what several makers say each rating suits.

Are watches waterproof? No. Standards and most makers say water resistant, because no seal gives permanent, absolute protection. The US FTC's old watch guides advised against calling a watch waterproof and were rescinded in 1999, so that is history, not a current ban. A few makers, such as Rolex in its Oyster Perpetual user guide, still use the word and pair it with care instructions.

What does 10 bar mean for water resistance? 10 bar water resistant means a test pressure of about 10 bar, roughly 100 m of still water, also written 10 ATM. It is a static laboratory rating, not a depth. Makers describe swimming at this rating, several add snorkelling or skin diving, and none of the makers checked lists scuba for it. Seals age, so the rating wears down.

Is a 100 m water resistant watch safe for swimming? Several makers say yes (Casio, Longines, Seiko, Timex), and Oris says 10 bar or more may be worn in water. That assumes seals in good condition and a closed crown, and makers cite soap, heat, steam and knocks as risks. Casio, Citizen, Longines and Seiko do not recommend scuba at this rating. Follow your own watch's manual.

What is 5 bar water resistant? About 50 m, or 5 ATM. Makers disagree about swimming: Casio's manuals, Citizen, Longines, Orient, Seiko and Timex describe it, with Longines and Timex saying shallow or light, while Oris says watches below 10 bar must not be worn in water. Rain and hand washing are common ground. Check your watch's own guidance.

How often should a watch's water resistance be tested? Makers differ. Aquastar says roughly every couple of years for a watch used in water, Casio's manuals say replace gaskets about every two or three years, Oris says annually, and Rolex and Seiko say periodically with no figure. A factory test is a snapshot, a hard knock can affect the seal, and a professional does the check. Follow your own watch's interval.

Maker pages and standards listings used in the tables were checked on 9 October 2026.

Prices and specifications checked October 2026. Tell us if something has changed.

Related reading

• What is a field watch?
• Sapphire crystal vs mineral glass
• The Vannin Field Watch
• Vannin watch care
• Why we chose a field watch for our first watch
• More articles