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The quick verdict
The bottom line: The F-91W is the icon – the one everyone recognizes, the best seller, the classic. The F-105W is the better watch in the dark, with a bigger display and a far superior backlight. Buy the F-91W for the legend, the F-105W for actually reading the time at night.
Check the F-91W price on Amazon | Check the F-105W price on Amazon
Introduction
Put the F-91W and F-105W side by side and most people cannot tell them apart. Same black resin case, same retro LCD, same three-pusher layout, same twenty-bucks-and-change price. But wear them for a week and the differences show up – mostly after sunset. I have owned and worn both, and my comparison video breaks down exactly where they diverge and which one deserves your wrist.
Watch: the full video comparison
If you have not read it yet, my full F-91W review covers the icon in depth, and my fake-spotting guide shows how to check that the one you buy is genuine.
Price and where to buy
Both watches live in the $15 to $30 range. The F-91W is usually a few dollars cheaper and far easier to find – it is one of the best-selling watches in history, so every retailer stocks it. The F-105W costs slightly more and can be harder to track down in some regions, which is worth knowing before you set your heart on it.
Fakes: the F-91W is one of the most counterfeited watches on earth. The F-105W gets faked less often, but the same checks apply. Run through my fake-spotting guide before you buy either.
Head-to-head: the differences that matter
| F-91W | F-105W | |
|---|---|---|
| Case | ~33.5 mm wide, 8.5 mm thick | Slightly larger, ~37.5 mm wide |
| Display | Smaller digits | Larger digits, easier to read |
| Backlight | Dim green LED glow | Electroluminescent panel, much brighter |
| Battery | CR2016, ~7 years | CR2016, ~7 years |
| Water resistance | Water Resist (splashes) | Water Resist (splashes) |
| Weight | ~21 g | ~25 g |
| Functions | Alarm, stopwatch, auto calendar, hourly signal | Alarm, stopwatch, auto calendar, hourly signal |
| Price | ~$15-25 | ~$20-30 |
Display and backlight: the real decision
This is the whole comparison. The F-91W’s backlight is famously terrible – a dim green LED glow that barely illuminates the small digits. It is the watch’s worst feature, full stop.
The F-105W fixes it completely. Its electroluminescent backlight lights the entire display evenly and brightly – the classic Casio “illuminator” glow. At night there is no contest. The F-105W also has slightly larger digits, which helps readability for everyone, especially if your eyes are not what they were.
In daylight, both displays are crisp and legible. The difference only appears in the dark – but the dark is half your life.
Size and wearability
The F-105W is a touch larger than the F-91W – a few millimeters wider. On the wrist the difference is subtle; both are light, slim resin watches that disappear under a cuff. The F-91W’s smaller case suits very slim wrists slightly better, while the F-105W’s marginally bigger presence works well on medium wrists. Neither will overwhelm anyone – these are small watches by modern standards.
Features and functions
Functionally the two are near-twins: daily alarm, hourly time signal, 1/100-second stopwatch, auto calendar. The button layout and menu logic will feel instantly familiar if you have used either. Battery life is rated around 7 years on the CR2016 cell for both, and both are Water Resist – fine for rain and splashes, not for swimming.
Build quality
Both are black resin, both are tougher than they look, and both will survive years of daily abuse. The F-105W’s slightly larger case does not change the formula. Neither watch is trying to feel premium – they are honest plastic tools, and that is the point.
Which one should you buy?
Buy the F-91W if: you want the icon. It is the original, the best seller, the one with decades of cultural history. It is also cheaper and easier to find. If the backlight does not bother you – and for many owners it genuinely does not – this is the default answer.
Buy the F-105W if: you actually need to read your watch in the dark. The backlight alone justifies the small premium, and the larger display is a real everyday benefit. It is the better watch; it is just not the famous one.
My take: I reach for the F-105W more often as a practical watch, but the F-91W is the one with the story. At these prices, the honest answer is that owning both costs less than a single dinner out – and plenty of Casio fans do exactly that.
What about the F-91WB?
Casio also makes the F-91WB, a color variant of the F-91W with a more grown-up look. If you like the F-91W formula but want something slightly less stark than basic black, it is worth a look. I reviewed it separately on the channel.
Pros and cons
F-91W pros:
- The icon – unmatched history and recognition
- Cheapest of the pair, easiest to find
- Smallest and lightest
F-91W cons:
- Backlight is nearly useless
- Smaller digits
F-105W pros:
- Excellent electroluminescent backlight
- Larger, easier-to-read display
- Same legendary reliability and battery life
F-105W cons:
- Slightly more expensive
- Harder to find in some regions
- Lacks the F-91W’s cultural status
FAQ
What is the main difference between the F-91W and F-105W?
The backlight and display size. The F-105W has a bright electroluminescent backlight and larger digits; the F-91W has a dim LED glow and smaller digits. Everything else – functions, battery, water resistance – is essentially the same.
Is the F-105W just a bigger F-91W?
Mostly, yes, with the upgraded backlight being the meaningful difference. Same design language, same resin build, same feature set, slightly larger case.
Which one is more accurate?
Both use standard Casio quartz movements accurate to about 15-30 seconds per month. Neither has atomic timekeeping – for that, step up to the GW-M5610U.
Are fake F-105Ws common?
Less common than fake F-91Ws, but they exist. The F-91W is one of the most counterfeited watches in the world, so check any purchase with my fake-spotting guide.
Can I swim with either watch?
No. Both are rated Water Resist, which covers splashes and rain only. For a swim-proof Casio at a budget price, look at the G-Shock squares.
F-91W vs F-105W – which is the better value?
The F-91W wins on pure price and availability. The F-105W wins on usability thanks to the backlight. The price gap is only a few dollars, so value comes down to whether you care about reading the time in the dark.
Final verdict
The F-91W is the legend and the F-105W is the better night watch. There is no wrong answer at twenty dollars – but if I could only keep one, the F-105W’s backlight would win me over. The F-91W earned its fame; the F-105W earned its place on my wrist.
Check the F-91W price on Amazon | Check the F-105W price on Amazon