Seiko Prospex SPB143 vs Seiko Prospex SPB155 (Baby Alpinist)

Side-by-side comparison of specifications and features

SeikoProspex

SPB143

SeikoProspex

SPB155 (Baby Alpinist)

Key Differences

Best Value

Seiko Prospex (Ref. SPB155 (Baby Alpinist))

Starting from $447

Slimmest

Seiko Prospex (Ref. SPB155 (Baby Alpinist))

12.9mm thick

Biggest Price Drop

Seiko Prospex (SPB143)

-3.1% in 30 days

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 SPB143

Balanced

Round · 40.5mm · 47.6mm lug-to-lug

Optimal proportions for most wrists

Case: 40.5mmLug-to-lug: 47.6mmThickness: 13.2mm

Open this size in the full fit chart →

Watch B

Seiko Prospex SPB155 (Baby Alpinist)

Balanced

Round · 38mm · 46mm lug-to-lug

Optimal proportions for most wrists

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

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

$1,200

New

$1,399

Used

$949

Seiko Prospex

MSRP

$725

New

$447

Used

$398

MSRP New (Amazon) Used (eBay)

Comparison of Seiko Prospex, Seiko Prospex
Specification	Seiko Prospex	Seiko Prospex
Pricing
MSRP	$1,200	$725
New Price	$1,399	$447
Used Price (Low)	$949	$398
Used Price (High)	$1,890	$5,250
30-Day Trend	↓ -3.1%	↑ +70.2%
Used Price Range	$949 - $1,890	$398 - $5,250
Identity
Reference	SPB143	SPB155 (Baby Alpinist)
Nickname	N/A	N/A
Style	Diver, Tool	Field, Sports, Tool
Release Era	2020s	2010s
Dimensions
Diameter	40.5mm	38mm
Thickness	13.2mm	12.9mm
Lug Width	20mm	20mm
Lug to Lug	47.6mm	46mm
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	Sapphire Crystal
Water Resistance	200m (diving)	200m (diving)
Bezel	Unidirectional rotating	Fixed
Dial
Dial Color	Gray	Green
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?

Seiko Prospex SPB143 and Seiko Prospex SPB155 (Baby Alpinist) can look close on a spec sheet, yet the tradeoffs that matter most are usually wrist presence versus easier fit, diver character versus field versatility, entry price versus premium finishing or specs. Treat it as a value-versus-upgrade decision — confirm the extra spend solves a problem you will notice every week.

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 SPB143 if you prefer more dial presence and a larger case feel; choose Seiko Prospex SPB155 (Baby Alpinist) if you want a smaller case footprint on the wrist.

Choose Seiko Prospex SPB143 when

Seiko Prospex SPB143 is a better fit for buyers who want more wrist presence, mechanical-watch enthusiasts, diver styling.

Choose Seiko Prospex SPB155 (Baby Alpinist) when

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

Key Differences

Movement and upkeep

Seiko Prospex SPB143: automatic movement

Seiko Prospex SPB155 (Baby Alpinist): 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 SPB143: 40.5mm · L2L 47.6mm · 180g

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

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 SPB143: 200m

Seiko Prospex SPB155 (Baby Alpinist): 200m

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

Price and value

Seiko Prospex SPB143: $987

Seiko Prospex SPB155 (Baby Alpinist): $447

There is a real price gap here — treat the more expensive option as an upgrade decision and confirm whether the extra spend buys something you will notice in weekly use.

Style and use case

Seiko Prospex SPB143: diver

Seiko Prospex SPB155 (Baby Alpinist): field

Seiko Prospex SPB143 leans more diver, while Seiko Prospex SPB155 (Baby Alpinist) pulls toward field use case — pick the one that matches how you will actually wear it.

Crystal and materials

Seiko Prospex SPB143: sapphire crystal · steel

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

Materials are broadly similar, so finish, fit, and price will matter more than the materials list alone.

Choose Seiko Prospex SPB143 If...

You prefer more dial presence and a larger case feel.
You are specifically shopping for a diver style watch.
You are comfortable paying more for a stronger feature set.

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.
You want the lower current entry price.

Price and Value Notes

Seiko Prospex SPB155 (Baby Alpinist) is often the value play at current pricing, while Seiko Prospex SPB143 makes more sense if you will use its extra features regularly.

There is a real price gap here — treat the more expensive option as an upgrade decision and confirm whether the extra spend buys something you will notice in weekly use.

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 $987 · New & used listings

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Seiko Prospex

Check Price on AmazonOpens in new tab · Price may vary

Check Price on eBayFrom $851 · 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 47.6mm, 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 $540 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.