Prospex Alpinist

Ref. SPB503

Case diameter: 39.5 mm; Manufacturer spec
Lug-to-lug: 46.4 mm; Manufacturer spec
Thickness: 12.7 mm; Manufacturer spec
Lug width: 20 mm; Manufacturer spec

Retail price $995 (US, Oct 2026)

Your wristIdeal fit

Wrist flat: 55.1 mmLug-to-lug: 46.4 mm

How the Prospex Alpinist wears

Its lugs add 6.9 mm to the 39.5 mm case, close to the 7.1 mm typical across the almanac, so its diameter is a fair guide to how it wears.

On our fit model it sits best on wrists from 6.5" to 7.75" (16.5–19.7 cm); below 6.5" the lugs start to reach the edge of the wrist.

At 12.7 mm thick it is thicker than 81% of the 26 other field watches we've measured, so expect it to sit tall on the wrist.

Its 20 mm lug width is one of the most common strap sizes; 104 other watches here share it, so aftermarket straps are easy to find.

Will the Prospex Alpinist fit your wrist?

With a 46.4 mm lug-to-lug, here is how it wears across common wrist sizes. We estimate the flat top of each wrist from its circumference; measure yours for a closer answer in the fit finder.

Wrist	Flat width (est.)	Fit
6"	47.2 mm	Lugs overhang
6.5"	51.2 mm	Ideal fit
7"	55.1 mm	Ideal fit
7.5"	59.1 mm	Ideal fit
8"	63 mm	Wears small

Specifications

Reference: SPB503
Collection: Prospex
Status: In production
Introduced: 2025
Case material: stainless steel (super-hard coating)
Crystal: sapphire (magnifier)
Water resistance: 200 m
Bezel: internal rotating compass bezel
Dial: teal
Strap / bracelet: stainless steel bracelet, three-fold clasp
Weight: 147 g
Style: Field, Sport

Movement

Caliber: Seiko 6R55
Type: automatic
Power reserve: 72 hours
Jewels: 24
Accuracy: +25/-15 s/day

3 other watches use the Seiko 6R55

Takes 20 mm straps. See other 20 mm watches and straps.

More Prospex references

Watches that wear the same size

Other watches within 1.5 mm of its lug-to-lug.

Same 20 mm lug width

All 20 mm watches

These take the same straps as the Prospex Alpinist.