What temperature can a watch withstand?

Two answers circulate. One says a watch is rated to 60°C, so anything below that is fine, a hot tub included. The other says heat is bad for watches, full stop. Neither holds up against the documents. The 60°C limit is real, but it is a limit for running, and the makers who print it also ban hot baths that sit well below it. Below, nine published limits are set side by side, then checked against the hot places a watch actually ends up.

What the makers publish

Few mechanical watch makers print a temperature range at all. The ones that do agree closely. Here is every limit we could read in a maker's own document, with the one secondhand figure marked as such.

First, 60°C is the ceiling on every traditional watch in the table, from a Casio digital to a Grand Seiko Spring Drive.

Second, the accuracy band is much narrower. Seiko quotes its 5R65 at ±15 seconds a month "only if worn on the wrist in a temperature range of 5°C to 35°C", and Citizen quotes the E365 at ±15 seconds a month "when worn at normal operating temperatures between +5°C (41°F) and +35°C (95°F)". Outside it the watch runs, but its rate is no longer promised. Our answer on quartz accuracy explains where that monthly figure comes from, and the one on mechanical accuracy gives the equivalent for a spring-driven watch.

Third, smartwatches are the cautious end. A standard Apple Watch is designed to work at 0 to 35°C, the same top figure Seiko uses for its accuracy band, and Garmin stops at 45°C. Our guide to smartwatches against mechanical watches covers the other trade-offs.

Omega's two figures, and which one to use

Search for this question and the most quoted figure is Omega's: -20 to +70°C. Chronocentric's Omega technical page attributes it to Omega, says it comes from the oils in the mechanical movements, and adds that the figure means the temperature inside the watch, not the air around it.

Omega's own customer service page today says something more conservative: "The optimum operating conditions for your timepiece are between 0°C (or 32°F) and 60°C (or 140°F). Use outside this temperature range may affect the performance of your watch." Use the second: it is what the maker publishes now, it agrees with Seiko and Citizen at the top end, and the 70°C figure reached us only secondhand. What lubricants a movement carries, and why they set a limit, is in our answer on which watch oil goes where.

The Chronocentric point about internal temperature still holds: the limits describe the watch, not the weather. A watch lying on a sunny dashboard can be far hotter than the air in the car, as the figures below show.

The hot places watches actually end up

Here are the situations behind most of these searches, each with a measured or regulated figure.

The car figures come from a 2018 study by Arizona State University and UC San Diego researchers, run on three summer days with temperatures above 100°F in Tempe, Arizona. It is a hot-climate worst case, but makers single out the dashboard anyway: Citizen's manual warns against charging an Eco-Drive "on the dashboard of a vehicle", and Casio's says "Never leave your watch on the dashboard of a car, near a heater, or in any other location that is subject to very high temperatures."

The sauna figure is the range a 2018 Mayo Clinic Proceedings review by Laukkanen and colleagues describes for Finnish sauna bathing. The air is well above the ceiling, so the only question is how far the watch heats toward it.

The hot tub figure is a safety cap for people, not watches: the US Consumer Product Safety Commission says hot tub water "should never exceed 104 degrees Fahrenheit". So the hottest legal hot tub sits 20 degrees under the watch makers' 60°C. That is where the "within spec" argument comes from.

Why hot water has its own rule

If temperature were the only issue, a 40°C bath would be safe. The makers say otherwise. Seiko's handling cautions for the 5R65 and the 4R34 both say "Do not wear the watch while taking a bath or a sauna", and give the reason: "Steam, soap or some components of a hot spring may accelerate the deterioration of water resistant performance of the watch." Casio's guide says not to wear the watch "while in a heated swimming pool, sauna, or any other high temperature/high humidity environment". Citizen's E365 manual bans the sauna on different grounds: "there is the risk of burns", to you, from the hot metal on your wrist.

The water resistance is what goes. Seiko names the parts: a water resistant watch may lose performance "because of deterioration of the adhesive on the glass or gasket". A water resistance rating is a pressure rating; it says nothing about hot water, as our water resistance guide explains and our answer on showering with a watch works through rating by rating. Omega's warning against "wide temperature variations" covers the other half: going from hot to cold fast. If moisture has already got in, our answer on fog under the crystal says what to do in the next hour.

So take the watch off for a hot tub, even though the number is in range. A 300 m dive watch is no exception, because its rating was never a heat rating.

What heat does to each kind of watch

The documents name a different weak point for each kind of watch.

• Solar quartz. Citizen warns against charging "at a high temperature (about 60°C (140°F) or higher)" because it "may cause the movement to malfunction", and gives two examples: too close to a lamp, and a car dashboard. A solar watch left on a sunny sill to charge is heated and charged at once. Our Eco-Drive page covers how the cell and capacitor work.
• Digital and LCD. Casio says time above 60°C "for long periods can lead to problems with its LCD", and that the display may become hard to read above 40°C.
• Battery quartz. Citizen's general caution is that the watch "may stop or the function of the watch may be impaired in extremely high or low temperature". If it stops after a hot day and does not restart once cool, our page on a stopped quartz watch goes through the causes in order.

The cold end of the range

The bottom of the range is -10°C for Seiko, Grand Seiko and Citizen, and 0°C for Omega and Apple. Seiko adds one rule for its 5R65 Spring Drive: "Under a low-temperature condition (below 0 °C), always keep at least one-sixth of the watch power shown by the power reserve indicator." Our Spring Drive page covers the system, and our answer on cold weather and watch rate gives the figures for how far quartz and mechanical watches drift.

What to do after a watch got hot

1. Let it cool in the air. Not under a cold tap or in a fridge: that is the "wide temperature variation" Omega warns against.
2. Look under the crystal. Mist or droplets mean moisture got in, and that is urgent.
3. Check the time over two or three days. A rate that has moved noticeably from its usual figure means something changed. For an LCD, check the display reads normally once cool.
4. Keep it dry until it is tested. One long spell of heat, such as a sauna or a dashboard in summer, is a reason to have the seals checked before you next swim in it. Our answer on pressure testing covers the test.

For storage, Seiko lists "places where the temperature drops below 5°C or rises above 35°C for a long time" among the places to avoid. A drawer indoors meets that; a glovebox or a sunny windowsill does not. Our guide to watch storage has the rest.

When this answer stops applying

• Your watch's own manual says something else. If your maker prints a different range, use that one.
• The watch is vintage. The published ranges describe new watches with fresh gaskets. A watch whose seals have not been replaced in years has no reliable rating for heat or water, whatever it once had.
• It is a smartwatch or fitness watch. The limits vary by model and are lower.
• The heat is brief and dry. A watch worn in a hot street is the case the operating range is written for. The ceiling matters when a watch is left somewhere hot.

For everything else the answer is short: under 60°C to run, 5 to 35°C to keep its rated accuracy, and off your wrist for saunas, hot tubs and steam, whatever the dial says about depth.