The Casio F-91W has been in continuous production since 1989 and is routinely described as one of the best-selling watches ever made. It costs less than a takeaway and it keeps better time than watches costing a hundred times more. It is worth understanding why — and where it genuinely falls short.
What you are actually buying
The F-91W is a resin-cased digital watch, roughly 38mm × 33mm, weighing about 21 grams. It has an auto-calendar, a daily alarm, an hourly chime, a 1/100-second stopwatch and a micro-light. Quoted accuracy is around ±30 seconds a month, and quoted battery life is seven years.
That last figure is the one people underestimate. A seven-year battery in a watch this cheap means the running cost is close to zero.
The strengths
It is genuinely light
At around 21g you stop noticing it. For anyone who finds steel watches heavy — or who wants something to sleep or train in — this matters more than any spec.
The alarm actually works
Unlike many cheap digitals, the F-91W's alarm is loud enough to wake you and the hourly chime is easy to toggle. It is a functional travel alarm strapped to your wrist.
It is easy to live with
The resin strap is comfortable, replaceable and cheap. The buckle is plastic and will eventually wear out, but replacements are widely available.
The honest weaknesses
The backlight is poor
The F-91W uses a single small LED, not an electroluminescent panel. In practice it lights the bottom-left of the display and leaves the rest dim. If night legibility matters, the A168 with its EL backlight is a better buy.
Water resistance is minimal
The F-91W is splash resistant only. It is not rated for swimming or showering. The case back is a press-fit and the pushers are not sealed against pressure.
The resin strap is the failure point
Cases and modules routinely outlive straps. Expect the strap or buckle to be the first thing to go, typically at the lug holes. Replacement straps are inexpensive and fitting one takes a spring bar tool and two minutes.
Variants worth knowing
- F-91W-1 — the standard black resin original.
- F-91WS — coloured resin variants, including blues and pastels.
- F-91WM — variants with patterned or metallic-look cases and bands, such as the F-91WM-7ADF.
- A158 / A168 — the steel-bracelet squares, if you want the same era of design in metal.
Module and functions are essentially shared across the F-91W family; the differences are cosmetic. Buy on the finish you prefer.
Setting it: the part everyone gets stuck on
The F-91W has three buttons. The lower-left cycles modes, the upper-left toggles and adjusts, and the lower-right advances values. To set the time, hold the upper-left button in timekeeping mode until the seconds flash, then use the mode button to move between fields and the lower-right to change them. To switch between 12 and 24-hour display, press the lower-right button while in timekeeping mode.
Is it still worth buying in 2026?
Yes, with a clear expectation. It is not a watch that will impress anyone, it will not survive a swim, and its light is bad. What it will do is tell the time accurately for the better part of a decade, weigh nothing, and cost so little that losing it is an inconvenience rather than a loss.
If you want the same design language with better water resistance and a far better light, look at the G-Shock DW-5600 instead — the spiritual successor at three or four times the price.
Browse the current Casio collection for stock and finishes.
Frequently asked questions
► Is the Casio F-91W waterproof?
No. It is splash resistant only — rain and handwashing are fine, but it is not rated for swimming, showering or diving.
► How long does the F-91W battery last?
Casio quotes approximately seven years under normal use. Replacement batteries are inexpensive and widely available.
► How do I set the time on an F-91W?
Hold the upper-left button in timekeeping mode until the seconds flash, use the lower-left mode button to move between fields, and the lower-right button to change the value.
► Can you replace the F-91W strap?
Yes. The strap is the usual first component to fail and replacements are cheap. Fitting one requires only a spring bar tool.
