Review: Casio’s F-91W Is Quite Possibly the Best $20 Watch Ever Made

There’s a short list of objects so perfectly conceived that they’ve never needed any updating. The Bic lighter. The Post-it note. The Pilot G-2 pen. And sitting comfortably on that list, the beloved Casio F-91W.

Let’s start with a little bit of history here because Casio’s story starts not with watches, but with a cigarette ring. In the late 1940s, Tadao Kashio, a lathe operator running a small machine parts business in Tokyo, noticed that Japanese office workers had no time for proper smoke breaks. His solution: a small finger ring with a conical holder that let you smoke hands-free, down to the last drag. Of course, it sold like crazy, and the profits rolled right into Casio’s next idea: the electric calculator. And the calculator funded everything that followed.

By 1974, Casio had shrunk their electronics down to wrist-size with the Casio Tron, the brand’s first watch, which already packed a quartz movement, integrated circuit, and automatic calendar into a case. From there, it was a decade-plus of refinement — smaller, cheaper, more efficient — cycling through some 30 models before designer Ryūsuke Moriai, in his very first project for the company, landed on the now iconic F-91W in 1989.

It looked almost identical to several watches before it. And yet it became the best-selling watch in the world, moving 3 million units a year since launch. For context, that’s more than three times Rolex’s annual output.

Of course, part of the F-91W’s legend is darker. The U.S. government identified it as a preferred tool of al-Qaeda operatives, who used its reliable countdown timer to detonate improvised explosive devices. Guantanamo Bay briefing documents called it “the sign of al-Qaeda.” In fact, Casio watches were cited nearly 150 times in detainee assessments. At the height of the War on Terror, just wearing one through an airport was enough to earn extra scrutiny, ironically enough, even as many of the officials doing the scrutinizing wore one themselves.

Worn by world leaders and warfighters, hipsters and terrorists, watch nerds and eight-year-olds. That’s the F-91W. 

We’ve been wearing the watch for decades and figured it was due time this wrist icon deserved the spotlight for its own individual review. So, without further ado, let’s get into it.

The first thing that hits you when you strap the F-91W on for the first time is just how little is there. At 21g total, this thing practically floats on your wrist. After years of handling steel-cased divers, field watches, and G-SHOCKs, the F-91W feels almost absurdly light. Not necessarily in a cheap way per se, but in a way that makes you wonder why we tolerate heavy watches at all.

It’s also smaller than most people expect on paper. At 35.2mm wide and 38.2mm lug-to-lug, it reads as a tiny watch in spec form. On the wrist, the four corner bumpers (these small resin cushions that flare out at each corner of the case) add just enough visual mass that it doesn’t disappear entirely, even on larger wrists. We’ve seen this watch look completely at home on everyone from slim-wristed college students to thick-armed military guys, which, as many watch enthusiasts know, is much rarer than you’d think.

It doesn’t try to remind you of anything else in the watch world, because it essentially is the reference point. This is what your brain draws when someone says the words “digital watch.” And that’s most certainly not an accident. It’s the result of a design that has been iterated, refined, and ultimately left alone for over 35 years because there was nothing left to fix.

The case itself is resin — basically all of it, save for the stainless steel caseback and the three side-mounted pushers. Measuring 35.2mm wide, 38.2mm lug-to-lug, and just 8.5mm thick, it’s one of the slimmest watches you’ll find at any price point. That thinness is a real asset under a sleeve, and combined with the 21-gram weight, it makes the F-91W the rare watch you can actually forget you’re wearing, seen here on our wearer’s 6.75” wrist for reference.

The four corner bumpers deserve more credit than they typically get. They protect the pushers during impacts by recessing them slightly into the case architecture. It’s a functional design choice that also happens to give the watch its distinctive silhouette. Left side gets two pushers (Light/top, Mode/bottom), right side gets one (Alarm/24hr toggle). And all three click with satisfying positive feedback.

There’s no real bezel to speak of here. It’s just the faceplate’s black surround printed with “WATER” and “RESIST” flanking a red “WR” badge at the 6 o’clock position. Blue accent lines frame the display above and below. It’s retro-graphic in the absolute best way possible, and the red-yellow-blue color language gives the watch a personality that a fully blacked-out case alone never could.

The caseback is stainless steel, secured by four small screws, with the module number (593) stamped at the center alongside basic production info. Nothing flashy; purely utilitarian, which is entirely appropriate.

Water resistance is rated at 30m, which technically means splash-proof by ISO standards. In practice, the F-91W has survived far worse in the hands of construction workers, soldiers, and swimmers worldwide. We wouldn’t take it diving, but we wouldn’t stress over a rainstorm or a sweaty gym session either.

And while this review is focused on the F-91W, we thought it was worth taking a quick moment to look at the F-91W’s “cousin,” the A158W. Different watch, same Module 593 heartbeat inside. The A158W swaps the resin case and strap for a fully stainless steel construction with a more angular, faceted case, and it’s the closest thing you’ll get to a steel version of the F91.

The LCD display on the F-91W is an absolute masterclass in information density at small scale. The main time display features large, chunky digits front and center, and is flanked by the day abbreviation top-left, date top-right, and seconds running in smaller numerals to the right of the hours and minutes. AM/PM indicator, alarm status, and hourly chime indicator round out the readout. It’s everything you need, and nothing you don’t.

The display sits behind a resin/acrylic crystal, and we’ll say upfront, it will scratch. That’s just the reality of acrylic at this price point, and anyone who’s owned one for more than a few months knows it. On the flip side, acrylic is shatter-resistant and remarkably clear when new, and given that a full replacement watch costs about $20, it’s hard to lose too much sleep over it. 

Legibility is excellent straight-on, and it also holds up reasonably well at moderate angles. It’s certainly better than the reading experience on some far more expensive digital watches. And in direct sunlight, the positive LCD display is crisp and easy to read.

There is obviously no lume here in the traditional sense. What you get instead is a single green LED mounted to the left side of the display, activated by pressing the top-left pusher. And we’ll be straight with you here: it’s bad. The illumination is uneven, heavily favoring the left side of the screen, leaving the right side noticeably dimmer. It functions, technically, but even calling it adequate feels generous. This is the F-91W’s most consistent criticism across the community, and it’s definitely valid. If you regularly need to read the time in the dark, plan accordingly.

Also, one really fun detail: hold the right pusher for three seconds in timekeeping mode and the display reads “CASIo,” which is Casio’s built-in anti-counterfeiting measure. The fact that a watch this cheap watch has a counterfeit problem tells you everything about its cultural status.

Powering the F-91W is Casio’s Module 593, a quartz caliber that’s about as no-drama as a movement gets. It’s accurate to ±30 seconds per month by Casio’s own spec, and in practice, most units run considerably tighter than that. It’s powered by a single CR2016 coin cell rated for approximately seven years of life, which again, in actual real-world use often stretches even longer.

Features-wise, Module 593 covers daily alarm with a 20-second beep, hourly time signal, stopwatch with 1/100-second precision counting up to 59:59.99 with split time capability, and annual calendar (with the caveat that February is always treated as 28 days; there’s no leap year accommodation).

Compared to Casio’s own AE-1200, another cheap Casio we love, the 593 does lack world time and a more capable backlight. But to be fair, the 593 isn’t really trying to be that watch. It’s a distillation, exactly what you need, in the smallest possible package, running on a battery you’ll likely replace once or twice in a decade.

The integrated resin strap is 18mm at the case and tapers slightly toward the buckle. It’s soft out of the box, flexible, and comfortable immediately. There’s no real break-in required. The plastic pin buckle is minimal and branded with “CASIO” in small lettering.

The strap is integrated into the case rather than using spring bars, which means swapping it requires a bit more effort than a standard lug setup. That said, a surprisingly dedicated community has built up around putting the F-91W on NATO straps and aftermarket rubber bands – the r/F91Ws_on_NATOs subreddit has nearly 4,000 members for context.

Long-term wear on the original strap can result in hardening and cracking over time, which is a known limitation of the material. Replacement straps are cheap and widely available, so it’s a manageable issue rather than a deal-breaker.

So as we wrap our review, we once again ask the question; is the Casio F-91W worth it?

That question almost feels wrong to ask. At $30 retail through Casio’s site, and almost perpetually on sale for $20 on Amazon, the F-91W occupies a category where “worth it” isn’t really even the framework. The better question is: what does this watch do that nothing else can?

It disappears on your wrist. It runs for seven years without asking anything of you. It’s more accurate than most mechanical watches costing fifty times its price. It looks right in places that would embarrass a G-SHOCK, and it survives abuse that would rattle a fashion watch apart. 

And on top of all that function, it carries a cultural biography — from Casio’s calculator-funded origins, to the wrists of presidents and special operators, to the Guantanamo briefing docs — that no watch at this price, and honestly most watches at any price, can even come close to matching.

Now, the backlight is genuinely bad. The acrylic crystal will scratch. And the strap will eventually harden. These are real limitations worth knowing. But they’re also entirely beside the point for a watch that costs less than a decent lunch.

As we mentioned, we’ve been wearing this watch on and off for decades, and we can tell you what the community has been saying for 35 years: there’s something about the F-91W that just works. Not in a spec-sheet way. In an “I keep reaching for it” way. And that’s the whole story here.

Recap

Casio F91W

The Casio F-91W is one of those rare, perfectly designed objects that’s barely changed since 1989 — cheap, light, accurate, and somehow worn by everyone from world leaders to terrorists. After decades of wearing it, the verdict is simple: the backlight is bad and the crystal scratches, but at $20-30, none of that really matters.

Pros

• Extremely lightweight and comfortable on the wrist
• Classic, instantly recognizable digital watch design
• Highly accurate and reliable quartz movement
• Long seven-year battery life
• Clear and information-dense LCD display
• Clear and information-dense LCD display
• Slim case that easily fits under sleeves

Cons

• Weak and uneven LED backlight
• Acrylic crystal scratches easily
• Limited 30m water resistance rating
• Integrated strap makes swapping harder
• Resin strap can harden and crack over time
• Basic feature set compared to larger digital watches

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