Quick Answer
Same module, same price, same seven-year battery. The F-91W weighs 21 g on a moulded resin strap; the A158WA weighs 46 g on a steel bracelet and is 1.6 mm shorter end to end. Buy the F-91W to forget you are wearing a watch, the A158WA to wear one to an office.
These two are the same watch wearing different clothes. Casio gives both the same digital quartz module — ±30 seconds a month, a CR2016 rated for around seven years, a 1/100 stopwatch, a daily alarm and an auto-calendar — and charges $29.95 for either. Everything worth deciding is on the outside.
Specification Comparison
Casio F-91W
2 categories won
Casio A158WA
2 categories won
- Typical street price
- $30Even
- $30Even
- Movement type
- QuartzEven
- QuartzEven
- Caliber
- Not published
- Not published
- Power reserve
- Battery, approximately 7 years on a CR2016 (Casio specification)
- Battery, approximately 7 years on a CR2016 (Casio specification)
- Stated accuracy
- ±30 seconds per month (Casio specification)Even
- ±30 seconds per month (Casio specification)Even
- Case width
- 35.2 mm
- 33.2 mm
- Case thickness
- 8.5 mmWinner
- 8.2 mm
- Lug-to-lug
- 38.2 mm
- 36.8 mmWinner
- Crystal
- Resin glassEven
- Resin glassEven
- Water resistance
- Water Resistant (Casio publishes no depth rating)Even
- Water Resistant (Casio publishes no depth rating)Even
- Bracelet / strap
- Resin strap
- Stainless steel braceletWinner
- Weight
- 21 gWinner
- 46 g
- Style
- Digital · Everyday
- Digital · Everyday · Dress
- Recommended wrist
- Small · Medium
- Small · Medium
- Selection Score
- Not published
- Not published
Selection Time Verdict
Choose the Casio F-91W
Choose the F-91W if weight is the point. At 21 g and 8.5 mm it is the closest a watch gets to wearing nothing, and the moulded strap means there is no clasp to catch and no bracelet to size. It is also the one to hand a child.
Read the full reviewChoose the Casio A158WA
Choose the A158WA if the watch has to look like metal. The chrome-plated case and steel bracelet pass in places resin does not, its green LED lights the display better than the F-91W's lamp, and at 36.8 mm end to end it is the smallest footprint in this database — useful on a genuinely small wrist.
Read the full reviewThere is no better watch here, only a lighter one and a dressier one. The specification is identical where it counts and Casio publishes no depth rating for either, so neither goes swimming. What separates them is 25 grams and a bracelet: the F-91W disappears, the A158WA gets noticed. At thirty dollars each, owning both is not an extravagant position — and if you can only have one, decide by where you will wear it rather than by what it does.
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Frequently Asked Questions
Do the F-91W and A158WA use the same movement?
The same class of Casio digital quartz module, with the same published specification: ±30 seconds per month, a CR2016 rated for around seven years, a 1/100-second stopwatch with split timing, a daily alarm and an auto-calendar.
Can either one be worn swimming?
No. Casio publishes no depth rating for either reference — only the words 'water resistant', which in Casio's own scale means rain and hand-washing. The AE-1200WH is rated to 100 m and costs ten dollars more.
Which is better for a small wrist?
The A158WA, on the number that decides fit: 36.8 mm end to end against the F-91W's 38.2 mm. Both are small by any modern standard; the A158WA is simply the smaller of the two.
Updated September 9, 2026