Casio · Classic Digital · Ref F-91W-1
Thirty-five millimetres of resin that outlived everything.
Quartz module 593 in a 35mm resin case, with an alarm, a stopwatch, a calendar and a backlight, on a battery Casio rates for seven years. It has not needed to change.
Module readout
01 /
Module 593
Everything the F-91W does comes out of one part: Casio’s digital quartz module 593. It carries an alarm, a stopwatch, a calendar and an LED backlight, and Casio rates its battery at seven years.
That last number is the one that matters. Seven years between cell changes is longer than most people keep a phone, and it is why an F-91W tends to be found working in a drawer rather than found dead in one.
02 /
Resin and acrylic
The case is resin and the crystal is acrylic — not steel, not mineral glass, not sapphire. Acrylic scratches easily, and it also polishes out easily, which is a different relationship with damage than a sapphire watch offers.
The whole watch weighs almost nothing as a result. Casio rates it at 30m, which it describes as splash resistant: handwashing and rain, not swimming.
03 /
A 35mm case
At 35mm the F-91W is small by current standards, and that is a large part of why it still reads as a watch rather than as a gadget. It fits under a cuff and it does not announce itself.
Casio has built this reference in Japan-designed form since 1989 and still lists it today. Our figures come from Casio’s published specifications, not from testing a unit ourselves.
Specs
- Reference
- F-91W-1
- Case size
- 35mm
- Case material
- Resin
- Movement
- Quartz Module 593
- Caliber type
- Casio Digital Quartz (Battery)
- Crystal
- Acrylic
- Water resistance
- 30m (Splash Resistant)
- Power reserve
- 7-Year Battery
- Complications
- Alarm, Stopwatch, Calendar, LED Backlight
- Origin
- Casio (Japan)
Specifications as published by Casio. We research from manufacturer documentation and published sources rather than hands-on testing. Researched 2026-09-03.
Verdict
A 35mm resin digital on module 593 with a seven-year battery — the cheapest watch on this site that nobody argues about.
Strengths
- Casio rates the battery at seven years
- Alarm, stopwatch, calendar and backlight in one module
- 35mm and effectively weightless on the wrist
- Acrylic crystal scratches, but also polishes out
Trade-offs
- 30m rating is splash resistance, not swimming
- Resin case and strap will eventually perish
- The backlight is a single LED, not a full panel
- No date-and-day complication beyond the basic calendar
Buy it if
A beater, a travel second watch, or a first watch for someone who will lose it — and would not mind.
Skip it if
You want to swim in it, want a metal case, or want a display you can read in the dark without pressing a button.
FAQ
Casio rates the F-91W’s battery at seven years. That figure comes from module 593, the digital quartz movement inside, and it is the single spec that most explains the watch’s reputation for turning up in a drawer still running.
Sources
Researched and last updated 2026-09-03. We do not test watches in hand; every figure above is traceable to the manufacturer or the sources listed here.
Casio F-91W
Reference F-91W-1 · Under $50
Prices and availability change; the band above is a research figure, so check the current listing.
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