Head-to-Head Comparison

Updated September 5, 2026

Casio F-91W vs Citizen Promaster Sea Eco-Drive Diver

Casio's timepiece meets Citizen's diver

Quick Verdict

The Casio F-91W (Under $50) offers Casio Digital Quartz (Battery) precision in the tier below the Citizen Promaster Sea Eco-Drive Diver ($250–$500). The F-91W measures 35mm and is rated 30m (Splash Resistant). The Promaster Sea Eco-Drive Diver counters with Made in Japan craftsmanship and 200m (20 ATM) ISO 6425 water resistance. Both are exceptional watches for their respective tiers.

CasioF-91WUnder $50 Check price CitizenPromaster Sea Eco-Drive Diver$250–$500 Check price

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Casio

F-91W

Under $50

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Citizen

Promaster Sea Eco-Drive Diver

$250–$500

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Specifications Compared

Feature	Casio F-91W	Citizen Promaster Sea Eco-Drive Diver
Price	Under $50	$250–$500
Case Size	35mm	44mm
Movement	Quartz Module 593	Eco-Drive Caliber E168
Caliber Type	Casio Digital Quartz (Battery)	Citizen Eco-Drive (Solar Quartz)
Power Reserve	7-Year Battery	—
Water Resistance	30m (Splash Resistant)	200m (20 ATM) ISO 6425
Crystal	Acrylic	Mineral 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 Citizen's approach

The Casio F-91W features a Resin case at 35mm with Acrylic protection. The Citizen Promaster Sea Eco-Drive Diver offers Stainless Steel construction at 44mm with Mineral Crystal. Both represent their brand's distinct design philosophy and heritage.

⚙️

Movement & Performance

Edge: Casio

Quartz Module 593 vs Eco-Drive Caliber E168

The F-91W runs the Quartz Module 593 (Casio Digital Quartz (Battery), 7-Year Battery power reserve) at standard frequency. The Promaster Sea Eco-Drive Diver uses the Eco-Drive Caliber E168 (Citizen Eco-Drive (Solar Quartz), standard reserve) at standard. The F-91W edges ahead on power reserve.

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Wearability & Fit

Edge: Casio

35mm vs 44mm — different wrist presence

At 35mm, the F-91W wears more compactly on smaller wrists compared to the Promaster Sea Eco-Drive Diver at 44mm. Water resistance differs: 30m (Splash Resistant) vs 200m (20 ATM) ISO 6425.

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Value & Cost of Ownership

Edge: Casio

Casio sits in the lower tier

The Casio F-91W sits at Under $50 and the Citizen Promaster Sea Eco-Drive Diver at $250–$500. On the specs that outlast any price: the F-91W uses Acrylic with 7-Year Battery, against Mineral Crystal and a standard reserve on the Promaster Sea Eco-Drive Diver. Service intervals are typically 5-7 years for both.

💧

Water Resistance

Edge: Citizen

30m (Splash Resistant) vs 200m (20 ATM) ISO 6425

The F-91W is rated to 30m (Splash Resistant) while the Promaster Sea Eco-Drive Diver handles 200m (20 ATM) ISO 6425. The Promaster Sea Eco-Drive Diver 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.

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Citizen

Promaster Sea Eco-Drive Diver

Choose the Citizen Promaster Sea Eco-Drive Diver if you value Citizen Eco-Drive (Solar Quartz) technology, Made in Japan heritage, and 44mm proportions. At $250–$500, the Eco-Drive Caliber E168 with ample power reserve makes it a compelling choice.

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The Bottom Line

The Casio F-91W and Citizen Promaster Sea Eco-Drive Diver represent two distinct approaches to fine watchmaking — the Casio bringing Casio (Japan) tradition while Citizen delivers Made in Japan engineering.

Frequently Asked Questions

For water, the Citizen Promaster Sea Eco-Drive Diver is rated 200 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 Citizen Promaster Sea Eco-Drive Diver 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 Promaster Sea Eco-Drive Diver at 44mm with 200m (20 ATM) ISO 6425 is similarly capable. The F-91W uses Acrylic while the Promaster Sea Eco-Drive Diver uses Mineral Crystal.

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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.