Seiko Prospex SPB155 (Baby Alpinist) vs Seiko Prospex Samurai

Side-by-side comparison of specifications and features

SeikoProspex

SPB155 (Baby Alpinist)

SeikoProspex Samurai

SRPB51

Key Differences

Best Value

Seiko Prospex (Ref. SPB155 (Baby Alpinist))

Starting from $435

Slimmest

Seiko Prospex (Ref. SPB155 (Baby Alpinist))

12.9mm thick

See Both Watches on Your Wrist

Set your wrist circumference to compare relative case presence. Lug-to-lug is included when the catalog has it.

Your wrist

Medium (6.7″)

Watch A

Seiko Prospex SPB155 (Baby Alpinist)

Balanced

Round · 38mm · 46mm lug-to-lug

Optimal proportions for most wrists

Case: 38mmLug-to-lug: 46mmLug width: 20mmThickness: 12.9mm

Open this size in the full fit chart →

Watch B

Seiko Prospex Samurai

Balanced

Round · 43.8mm · 48mm lug-to-lug

Optimal proportions for most wrists

Case: 43.8mmLug-to-lug: 48mmLug width: 22mmThickness: 13.4mm

Open this size in the full fit chart →

Proportional guide only: wrist shape, strap articulation, bezel design, and case curvature change how a watch actually wears.

Price Comparison

Seiko Prospex

MSRP

$725

New

$435

Used

$461

Seiko Prospex Samurai

MSRP

$525

New

$550

Used

$589

MSRP New (Amazon) Used (eBay)

Comparison of Seiko Prospex, Seiko Prospex Samurai
Specification	Seiko Prospex	Seiko Prospex Samurai
Pricing
MSRP	$725	$525
New Price	$435	$550
Used Price (Low)	$461	$589
Used Price (High)	$5,250	$2,555
30-Day Trend	↑ +36.5%	↑ +9.1%
Used Price Range	$461 - $5,250	$589 - $2,555
Identity
Reference	SPB155 (Baby Alpinist)	SRPB51
Nickname	N/A	N/A
Style	Field, Sports, Tool	Diver, Tool
Release Era	2010s	2010s
Dimensions
Diameter	38mm	43.8mm
Thickness	12.9mm	13.4mm
Lug Width	20mm	22mm
Lug to Lug	46mm	48mm
Movement
Movement	Automatic	Automatic
Power Reserve / Battery	N/A	N/A
Accuracy	N/A	N/A
Case
Case Material	Stainless Steel	Stainless Steel
Crystal	Sapphire Crystal	Hardlex
Water Resistance	200m (diving)	200m (diving)
Bezel	Fixed	Unidirectional rotating
Dial
Dial Color	Green	Blue
Luminous	Yes	Yes
Community
Review Rating	N/A	N/A
In Collections	N/A	N/A
On Wishlists	N/A	N/A
Forum Threads	N/A	N/A

Which Should You Buy?

This Seiko Prospex SPB155 (Baby Alpinist) vs Seiko Prospex Samurai comparison is less about a universal winner and more about wrist presence versus easier fit, field character versus diver versatility. Start with fit first — case width and lug-to-lug usually matter more than secondary features if wrist comfort is a concern.

Bottom line

Fit is a real separator here — compare case width and lug-to-lug before deciding, especially if wrist comfort matters more than headline features. Choose Seiko Prospex SPB155 (Baby Alpinist) if you want a smaller case footprint on the wrist; choose Seiko Prospex Samurai if you prefer more dial presence and a larger case feel.

Choose Seiko Prospex SPB155 (Baby Alpinist) when

Seiko Prospex SPB155 (Baby Alpinist) is a better fit for smaller wrists, mechanical-watch enthusiasts, field styling.

Choose Seiko Prospex Samurai when

Seiko Prospex Samurai is a better fit for buyers who want more wrist presence, mechanical-watch enthusiasts, diver styling.

Key Differences

Movement and upkeep

Seiko Prospex SPB155 (Baby Alpinist): automatic movement

Seiko Prospex Samurai: automatic movement

Both use the same movement type, so maintenance differences are limited and fit or feature details should decide the purchase.

Size and wearability

Seiko Prospex SPB155 (Baby Alpinist): 38mm · L2L 46mm · 144g

Seiko Prospex Samurai: 43.8mm · L2L 48mm

Fit is a real separator here — compare case width and lug-to-lug before deciding, especially if wrist comfort matters more than headline features.

Water resistance

Seiko Prospex SPB155 (Baby Alpinist): 200m

Seiko Prospex Samurai: 200m

Water resistance is similar on paper, so focus on fit, features, and price instead.

Price and value

Seiko Prospex SPB155 (Baby Alpinist): $435

Seiko Prospex Samurai: $525

These two often land in a similar price band — which usually means fit, features, and current deal quality matter more than the sticker price.

Style and use case

Seiko Prospex SPB155 (Baby Alpinist): field

Seiko Prospex Samurai: diver

Seiko Prospex SPB155 (Baby Alpinist) leans more field, while Seiko Prospex Samurai pulls toward diver use case — pick the one that matches how you will actually wear it.

Crystal and materials

Seiko Prospex SPB155 (Baby Alpinist): sapphire crystal · steel

Seiko Prospex Samurai: Hardlex crystal · steel

Crystal choice can change long-term wear expectations — one may prioritize scratch resistance while the other keeps cost or vintage feel in check.

Choose Seiko Prospex SPB155 (Baby Alpinist) If...

You want a smaller case footprint on the wrist.
You are specifically shopping for a field style watch.

Choose Seiko Prospex Samurai If...

You prefer more dial presence and a larger case feel.
You are specifically shopping for a diver style watch.

Price and Value Notes

Seiko Prospex SPB155 (Baby Alpinist) usually offers the lower entry price — confirm current listings because marketplace pricing can move quickly.

These two often land in a similar price band — which usually means fit, features, and current deal quality matter more than the sticker price.

Where to Check Deals

Check current deals on Amazon and eBay using the buttons below — listing prices, seller quality, and condition can change quickly.

Check current deals on Amazon and eBay

Prices change often, so compare the latest listings and condition options before you buy.

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Seiko Prospex

Check Price on AmazonOpens in new tab · Price may vary

Check Price on eBayFrom $773 · New & used listings

Affiliate links — WatchCompared earns a commission on qualifying purchases. This doesn't affect your price.

Seiko Prospex Samurai

Check Price on AmazonOpens in new tab · Price may vary

Check Price on eBayFrom $643 · New & used listings

Affiliate links — WatchCompared earns a commission on qualifying purchases. This doesn't affect your price.

Comparison FAQ

Which one is better for smaller wrists?

Seiko Prospex SPB155 (Baby Alpinist) — it is 46mm lug-to-lug versus 48mm, and lug-to-lug is what decides whether a watch overhangs a smaller wrist.

Which is better for swimming or rough daily wear?

They are rated the same, so water resistance will not decide this. Choose on strap material and how much you mind scratching the case.

Is the more expensive one worth it?

Seiko Prospex SPB155 (Baby Alpinist) is the value pick at roughly $90 less. Pay more only if a specific difference above matters to you — otherwise the cheaper one is the smarter buy. Confirm live listings, since marketplace pricing moves.