Head-to-Head Comparison

Updated September 5, 2026

Casio F-91W vs Seiko 5 Sports 5KX

Two timepieces compared — Under $50 vs $250–$500

Quick Verdict

The Casio F-91W (Under $50) offers Casio Digital Quartz (Battery) precision in the tier below the Seiko 5 Sports 5KX ($250–$500). The F-91W measures 35mm and is rated 30m (Splash Resistant). The 5 Sports 5KX counters with Made in Japan craftsmanship and 100m (10 ATM) water resistance. Both are exceptional timepieces for their respective tiers.

CasioF-91WUnder $50 Check price Seiko5 Sports 5KX$250–$500 Check price

Transparency — We earn a small commission on purchases made through our Amazon links. This doesn't affect our editorial independence.

Casio

F-91W

Under $50

Check Price Full Review

Seiko

5 Sports 5KX

$250–$500

Check Price Full Review

Specifications Compared

Feature	Casio F-91W	Seiko 5 Sports 5KX
Price	Under $50	$250–$500
Case Size	35mm	42.5mm
Movement	Quartz Module 593	Automatic Caliber 4R36
Caliber Type	Casio Digital Quartz (Battery)	Seiko In-House Automatic
Power Reserve	7-Year Battery	41 Hours
Water Resistance	30m (Splash Resistant)	100m (10 ATM)
Crystal	Acrylic	Hardlex Crystal
Case Material	Resin	Stainless Steel
Origin	Casio (Japan)	Made in Japan

Category-by-Category Analysis

🎨

Design & Aesthetics

Edge: Draw

Casio's design language vs Seiko's approach

The Casio F-91W features a Resin case at 35mm with Acrylic protection. The Seiko 5 Sports 5KX offers Stainless Steel construction at 42.5mm with Hardlex Crystal. Both represent their brand's distinct design philosophy and heritage.

⚙️

Movement & Performance

Edge: Seiko

Quartz Module 593 vs Automatic Caliber 4R36

The F-91W runs the Quartz Module 593 (Casio Digital Quartz (Battery), 7-Year Battery power reserve) at standard frequency. The 5 Sports 5KX uses the Automatic Caliber 4R36 (Seiko In-House Automatic, 41 Hours reserve) at 21,600 vph (3 Hz). The 5 Sports 5KX offers a longer power reserve.

📏

Wearability & Fit

Edge: Casio

35mm vs 42.5mm — different wrist presence

At 35mm, the F-91W wears more compactly on smaller wrists compared to the 5 Sports 5KX at 42.5mm. Water resistance differs: 30m (Splash Resistant) vs 100m (10 ATM).

💰

Value & Cost of Ownership

Edge: Casio

Casio sits in the lower tier

The Casio F-91W sits at Under $50 and the Seiko 5 Sports 5KX at $250–$500. On the specs that outlast any price: the F-91W uses Acrylic with 7-Year Battery, against Hardlex Crystal and 41 Hours on the 5 Sports 5KX. Service intervals are typically 5-7 years for both.

💧

Water Resistance

Edge: Seiko

30m (Splash Resistant) vs 100m (10 ATM)

The F-91W is rated to 30m (Splash Resistant) while the 5 Sports 5KX handles 100m (10 ATM). The 5 Sports 5KX offers superior water resistance.

Our Verdict

Casio

F-91W

Choose the Casio F-91W if you prioritize Casio Digital Quartz (Battery) engineering, Casio (Japan) craftsmanship, and 30m (Splash Resistant) water resistance. At Under $50, it delivers Quartz Module 593 with 7-Year Battery power reserve.

Check Price on Amazon

Seiko

5 Sports 5KX

Choose the Seiko 5 Sports 5KX if you value Seiko In-House Automatic technology, Made in Japan heritage, and 42.5mm proportions. At $250–$500, the Automatic Caliber 4R36 with 41 Hours power reserve makes it a compelling choice.

Check Price on Amazon

Try Prime Free — Free Shipping on Both Watches Students & 18–24: start Prime for Young Adults free

The Bottom Line

The Casio F-91W and Seiko 5 Sports 5KX represent two distinct approaches to the timepiece category — the Casio bringing Casio (Japan) tradition while Seiko delivers Made in Japan engineering.

Frequently Asked Questions

The Seiko 5 Sports 5KX is the better buy if you want a mechanical movement; the Casio F-91W is the better buy if you want quartz accuracy with no servicing. For water, the Seiko 5 Sports 5KX is rated 100 m against 30 m, which is the difference between swimming and diving on one side and splashes on the other. On price, the Casio F-91W sits a band lower (Under $50 against $250–$500), so it is the cheaper way into the category. Neither is better at everything; the spec table above shows movement, case size, water resistance and crystal side by side so you can weigh what matters to you. We do not test units, so this is the makers' data, not a bench result.

The Casio F-91W offers better upfront value, sitting a tier lower at Under $50. However, the Seiko 5 Sports 5KX may justify its premium with superior finishing, heritage, or resale value.

Both are suitable for daily wear. The F-91W at 35mm with 30m (Splash Resistant) water resistance handles everyday situations. The 5 Sports 5KX at 42.5mm with 100m (10 ATM) is similarly capable. The F-91W uses Acrylic while the 5 Sports 5KX uses Hardlex Crystal.

More Comparisons

Citizen Tsuyosa Green vs Seiko 5 Sports

Sapphire and 50m against Hardlex and 100m

Hamilton Khaki Field Automatic vs Seiko 5 Sports

Same 100m rating, roughly triple the price

Casio Duro vs Seiko 5 Sports

Quartz diver or first automatic

Explore These Watches

Casio F-91W — Full Review Seiko 5 Sports 5KX — Full Review Browse All Guides

How This Page Was Made

Our comparisons are generated from a hand-maintained specification database and reviewed under our editorial standards. We use AI tools to assemble pages from that data. We don’t invent specs: every number traces back to the database, and when we correct an entry, the fix is applied site-wide. As an Amazon Associate, The Horologist earns from qualifying purchases.