Watch accuracy is often described in vague terms like "very precise" or "chronometer grade". The numbers are much more useful. This guide compares the main types of watch by how many seconds they typically gain or lose, explains the certification standards, and helps you decide how much accuracy you actually need.
Manufacturers quote accuracy as seconds gained or lost over a period: per day for mechanical watches, per month or per year for quartz. A rating of "±15 seconds per month" means the watch should stay within 15 seconds of the correct time, early or late, over 30 days. These figures are specifications, usually measured in controlled conditions. On your wrist, temperature, movement and age will change the result a little, as we explain in our guide to why watches lose time.
| Watch type | Typical accuracy | What stands behind it |
|---|---|---|
| Ordinary mechanical | A few seconds to about half a minute per day | Depends heavily on make, age and service |
| Certified chronometer (COSC) | −4 to +6 seconds per day | Independent testing of the movement in several positions and temperatures |
| Rolex Superlative Chronometer | −2 to +2 seconds per day | Tested again after the movement is cased |
| Master Chronometer (METAS) | 0 to +5 seconds per day | Eight tests, including resistance to strong magnetic fields |
| Standard quartz | About ±15 seconds per month | A 32,768 Hz crystal and a battery |
| Spring Drive | About ±1 second per day | A mechanical mainspring, regulated electronically |
| High-accuracy quartz | About ±10 seconds per year, or better | Temperature compensation or a selected crystal |
| Radio-controlled or GPS | Within about a second when synchronised | Corrected from an atomic time signal |
| Smartwatch | Within about a second | Time taken from a phone or network |
Treat these as manufacturer figures. Real-world results vary, and there are good and bad examples in every category.
A mechanical watch is a miniature machine run by a spring, gears and a balance wheel. It is remarkable that it can keep time at all, and a well-regulated one can beat a cheap quartz watch. But it will always drift, and by different amounts in different positions, at different temperatures and at different levels of spring tension.
The two best-known certifications are COSC, the Swiss chronometer testing body, and the stricter METAS Master Chronometer standard used by Omega. Rolex applies its own tighter limit of ±2 seconds per day to the finished watch. These numbers look small, but over a month a watch that gains 4 seconds a day is more than two minutes ahead.
A quartz watch counts the vibrations of a tiny crystal that oscillates 32,768 times per second. It is cheap, consistent and typically about 15 seconds a month out. That is more accurate than most mechanical watches, which is why quartz nearly wiped out mechanical watchmaking in the 1970s.
At the high end, thermo-compensated quartz movements measure temperature and correct for it, reaching around ±10 seconds a year. Citizen's Caliber 0100 claims one second per year, the most accurate claim we know of among wristwatches that do not rely on an outside signal.
Seiko's Spring Drive is an unusual hybrid. Like a mechanical watch, it is powered by a mainspring and has no battery, but instead of a balance wheel it uses a quartz oscillator and a small electromagnetic brake to regulate the speed. The result is a gliding seconds hand and an accuracy of about one second per day.
A solar watch is usually just a quartz watch with a rechargeable cell, so its accuracy is the same as ordinary quartz. Its advantage is that you rarely change the battery.
Radio-controlled watches go further. They receive a time signal from an atomic clock station, such as WWVB in the United States, DCF77 in Germany, MSF in Britain or JJY in Japan, and correct themselves automatically. GPS watches do the same using satellite signals and can also adjust for time zones. Manufacturers quote an error of one second in 100,000 years for such watches. That is a statement about the time source, not about the watch, which only keeps good time as long as it can regularly receive the signal. You can read about the references behind this in our guide to how atomic clocks work.
A smartwatch usually takes its time from a connected phone, which takes it from the network. It is therefore accurate to within about a second in normal use, and it changes time zone automatically when you travel. It does not have an independent claim to accuracy, but it rarely needs one.
For most people, the answer is "less than you think". A watch that is within a minute a month will never make you late. What matters more is consistency. A mechanical watch that gains exactly 3 seconds a day can be corrected or regulated, whereas a watch that runs erratically cannot.
If accuracy is important to you, there are three practical steps. Choose a quartz or radio-controlled watch, or a certified mechanical one. Keep it away from strong magnets. And check it against a reliable reference now and then, as we describe in our guide on how to calibrate a watch.