Casio Casio F91W-1 F91W-1

The Casio F91W-1 is an ultra-low-cost digital watch introduced in June 1989 as the successor to the F-87W. Built around Casio's quartz Module 593 in a lightweight resin case, it displays time, day, and date alongside a 1/100-second stopwatch, daily alarm, and hourly time signal. Its design has changed little since launch, and cumulative production has passed 100 million units, making it the best-selling watch in the world.

Casio introduced the F-91W in June 1989 as the successor to the earlier F-87W. It was designed by Ryūsuke Moriai, in what was his very first project for the company, according to hiconsumption reviewer Ian Rebello.

The watch's design has been left largely untouched since launch. Rebello notes the current F91W-1 "basically looks the same as one you could have bought when it first launched" decades ago, with production running at roughly 3 million units a year. Wikipedia puts cumulative production at more than 100 million units as of 2026, describing it as the most sold watch in the world.

The F91W has been worn by a broad range of public figures, including former U.S. President Barack Obama, Hyundai executive Chung Eui-sun, philanthropist Chuck Feeney, and Zapatista spokesperson Subcomandante Marcos, per Teddy Baldassarre's review.

The watch also became notorious during the U.S. War on Terror. According to declassified Guantanamo Bay documents cited on Wikipedia, the F-91W was flagged as "the sign of al-Qaeda," with Casio watches appearing in roughly 150 detainee assessments as one factor cited in continued detention decisions.

The F91W-1 runs on Casio's quartz Module 593, listed by both straphabit and hiconsumption in their respective specification tables. It drives a time, day, and date display along with a stopwatch capable of 1/100-second precision, counting up to 59 minutes, 59.99 seconds, per Wikipedia.

Beyond timekeeping, the module supports a daily alarm and an hourly time signal. Its calendar does not adjust for leap years, so per Wikipedia, February is always displayed with 28 days regardless of the actual year.

Casio rates the movement's accuracy at roughly ±30 seconds per month, according to Wikipedia. Power comes from a single CR2016 3-volt lithium button cell, rated for about seven years of service — a figure both straphabit and hiconsumption cite in their spec breakdowns, with owners commonly reporting longer real-world life.

The module also drives a green LED backlight, which hiconsumption reviewer Ian Rebello describes as "bad," with illumination that is "uneven" and "heavily favoring the left side" of the display.

At 21 grams, reviewers consistently describe the F91W-1 as disappearing on the wrist. Hiconsumption's Ian Rebello writes that it "practically floats on your wrist" and that its slim 8.5mm profile slides easily under a sleeve, adding that the design looks equally at home on slim-wristed students and larger-framed wearers alike — something he calls "much rarer than you'd think" for a watch to pull off.

Straphabit reviewer Nick Lehner had a similar reaction, admitting he "felt a little silly wearing it at first, but quickly adjusted," praising how "thin and light" it is to the point that it "almost disappears on the wrist."

Both reviewers note real limitations alongside the comfort. Rebello lists the acrylic crystal as prone to scratching — "just the reality" at this price point — and observes that the integrated resin strap eventually hardens and cracks with age, on top of the uneven backlight noted in the movement section.

Teddy Baldassarre lists the F91W-1's retail price at $22.95, noting it is frequently discounted to around $16 through mass retailers rather than dedicated watch dealers.

Unlike specialty timepieces, the F91W-1 is sold through general retail channels — mass merchants, department stores, and online marketplaces — alongside Casio's own site, reflecting its position as a basic consumer good rather than a boutique product.

Because of its low price and enormous production volume, counterfeits are common. Wikipedia notes that genuine units can be checked by holding the lower-right button for three or more seconds while in timekeeping mode, which displays "CASIo," or by pressing all three buttons simultaneously to enter a diagnostic test mode; authentic examples also tend to have better LCD viewing angles and plastic quality than fakes.

Buyers should also expect price to vary by variant — hiconsumption notes Casio's licensed PAC-MAN edition retails around $60, notably above the standard black F91W-1.