Casio F-91W: The Digital Watch Unchanged Since 1989
The Casio F-91W came out in June 1989 and its design has barely changed since. Its features, battery life, water resistance, designer and why it became famous.
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Short answer: The Casio F-91W is a resin-cased, three-button digital watch released in June 1989. It was designer Ryūsuke Moriai's first watch for Casio. With a battery that lasts about 7 years, an alarm, a 1/100-second stopwatch and a weight of 21 grams, it has been made almost unchanged for over thirty years. Cheap, tough and sold almost everywhere, it is one of the best-known watches in the world.
Almost everyone has seen an F-91W: on school desks, in the military, in offices and in news photos. This story covers where the watch came from, exactly what it can do, and how such a plain watch became so famous.
When did the F-91W come out, and who designed it?
The F-91W was released by Casio in June 1989 as the successor to the F-87W. Some sources give 1991, but that was an error; the watch came out in 1989.
Its designer was Ryūsuke Moriai. The F-91W was the first watch Moriai designed for Casio. He had joined the company in 1985 and went on to become chief designer of the G-Shock line.
The goal was simple: a legible, durable, accurate watch that anyone could afford. The F-91W met it so well that its design has barely changed since.
What are the F-91W's features?
Inside the F-91W is Casio's quartz module 593; the number is also stamped on the caseback. Here is what the watch can do:
- Time and calendar: hours, minutes, seconds, day and date. The calendar does not account for leap years, so February always has 28 days and the date needs a manual correction in leap years.
- Stopwatch: measures to 1/100 of a second up to 59:59.99, with split times.
- Alarm: a daily alarm that sounds for 20 seconds, plus an optional hourly beep.
- Light: a small green LED on the left side lights the display in the dark.
| Casio F-91W-1 | |
|---|---|
| Module | 593 |
| Battery | CR2016 lithium button cell |
| Battery life | About 7 years |
| Accuracy | About ±30 seconds per month |
| Case | Resin, stainless steel caseback |
| Dimensions | 38.2 × 35.2 × 8.5 mm |
| Weight | 21 g |
| Water resistance | "Water Resist": suitable for everyday use |
±30 seconds a month works out to roughly one second a day, better than many well-regulated mechanical watches. If you are curious about something far more precise, read our story on the Citizen Caliber 0100, accurate to ±1 second a year.
Is the F-91W waterproof?
Partly. The front reads "Water Resist", which means it can handle rain, hand-washing and splashes. But watches in this class are not suitable for swimming, showering or bathing. For a watch you will wear in the pool or the sea, look for a higher water-resistance rating given in metres.
Why is it so famous?
The F-91W's fame comes from several places at once:
- Price and availability: it is affordable and sold in almost every country. It regularly appears among the best-selling watches on large stores such as Amazon.
- A design that never changed: Casio calls the design "tried and true". The watch sold today is almost identical to the one from 1989.
- Famous wrists: there are well-known photos of Barack Obama wearing an F-91W before he became president.
- The sales legend: it is often said to sell millions a year, but Casio does not publish sales figures. So the claim that it is "the best-selling watch in the world" is not verified.
Where does the "terrorist watch" nickname come from?
The F-91W has a darker reputation too. In the mid-1990s it emerged that militants in Pakistan and the Philippines had learned to use it as a timer for improvised explosive devices, and for a while it was known as "the terrorist watch".
The watch also turned up often in the Guantánamo files leaked in 2011. According to NPR, it was mentioned nearly 150 times in the detainee assessments and was listed in some files as a reason for suspicion. The same report pointed out that these watches are sold in just about every street market in South Asia. A watch worn by millions of people clearly proves nothing on its own.
Versions of the F-91W
The classic model is the F-91W-1, with a black case and blue frame around the display. There are other versions too, such as the F-91WG with gold-coloured buttons and trim, and the F-91WM series with metallic-look cases. All of them share the same display layout and the same basic functions.
Where did the digital watch come from?
The F-91W arrived almost 20 years after the first digital wristwatches. The world's first digital electronic wristwatch was the Pulsar, unveiled by Hamilton in 1970; when it went on sale in 1972, the first gold model cost as much as a family car. We tell the Pulsar's story in Where is Hamilton from? The F-91W was one of the watches that put the same idea on everyone's wrist.
Frequently asked questions
When did the Casio F-91W come out? In June 1989. The year 1991, given in some sources, is wrong.
How long does the Casio F-91W battery last? Casio quotes about 7 years. The watch runs on a single CR2016 lithium button cell.
Can you swim with a Casio F-91W? It is not recommended. Watches marked "Water Resist" can handle rain and hand-washing, but are not suitable for swimming, showering or bathing.
How accurate is the Casio F-91W? About ±30 seconds a month, or roughly one second a day.
How can you tell a genuine Casio F-91W? The caseback carries the module number 593, and on newer examples holding down a button shows "CASIO" on the display. For more Casio stories, see our Casio page.
