Seiko SPB155 'Baby Alpinist'
Ref. SPB155 · In production
- Case38 mm
- Thick12.9 mm
- Lug-to-lug46 mm
- Water res.200 m
- MovementAutomatic
- CrystalSapphire
Overview
The Seiko SPB155 is a diver watch from the Prospex collection, part of the Seiko Baby Alpinist family. It has a 38 mm stainless steel case, 12.9 mm thick, 46 mm from lug to lug. Inside is a automatic movement (calibre 6R35) with 70 h of power reserve. You also get 200 m water resistance, a sapphire crystal and a bracelet.
Who it suits
- Wrists of roughly 15.5–17.0 cm (6.1–6.7 in), by our Watch Finder sizing guide
- Swimming, snorkelling and diving
- People who enjoy seeing a mechanical movement at work
Strengths
- Sapphire crystal resists scratches
- 200 m water resistance
- Screw-down crown helps keep water out
- 70 h power reserve survives a weekend off the wrist
- Compact 46 mm lug-to-lug suits smaller wrists
- Display caseback shows the movement
- Hacks and hand-winds, so it is easy to set
Written by Watch.co from the published specs below. These are not owner reviews.
Full specifications
Case
| Case diameter | 38 mm | seikowatches.com · 23 Oct 2026 |
|---|---|---|
| Thickness | 12.9 mm | seikowatches.com · 23 Oct 2026 |
| Lug-to-lug | 46 mm | seikowatches.com · 23 Oct 2026 |
| Case material | Stainless steel | seikowatches.com · 23 Oct 2026 |
| Crystal | Sapphire | seikowatches.com · 23 Oct 2026 |
| Anti-reflective coating | Anti-reflective coating on inner surface | seikowatches.com · 23 Oct 2026 |
| Caseback | Display (see-through) | seikowatches.com · 23 Oct 2026 |
| Water resistance | 200 m | seikowatches.com · 23 Oct 2026 |
| Screw-down crown | Yes | seikowatches.com · 23 Oct 2026 |
| Weight | 144 g | seikowatches.com · 23 Oct 2026 |
Dial
| Luminous material | LumiBrite | seikowatches.com · 23 Oct 2026 |
|---|---|---|
| Date | Date | our classification |
Movement
| Movement type | Automatic | seikowatches.com · 23 Oct 2026 |
|---|---|---|
| Calibre | 6R35 | seikowatches.com · 23 Oct 2026 |
| Made in-house | Yes | seikowatches.com · 23 Oct 2026 |
| Power reserve | 70 h | seikowatches.com · 23 Oct 2026 |
| Hacking seconds | Yes | seikowatches.com · 23 Oct 2026 |
| Hand-winding | Yes | seikowatches.com · 23 Oct 2026 |
Strap / Bracelet
| Bracelet / strap | Bracelet | seikowatches.com · 23 Oct 2026 |
|---|---|---|
| Lug width | 20 mm | seikowatches.com · 23 Oct 2026 |
Other
| US list price (MSRP) | $725 | seikowatches.com · 23 Oct 2026 |
|---|---|---|
| Production status | In production | seikowatches.com · 23 Oct 2026 |
| Style (our classification) | Diver | our classification |
| Nickname | Baby Alpinist | our classification |
Specs are summarised in our own words from the brand's product page. Each row links its source and the date we checked it. Fields we haven't verified are left out rather than guessed.
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Questions about the Seiko SPB155
How big is the Seiko SPB155?
The case is 38 mm wide, 12.9 mm thick and 46 mm from lug to lug.
What movement does the Seiko SPB155 use?
It uses the 6R35 calibre, a automatic movement with 70 h of power reserve.
Can I swim with the Seiko SPB155?
Yes. It is rated to 200 m.
Does the Seiko SPB155 have a date?
Yes, it shows the date.
How much is the Seiko SPB155?
The US list price was $725 on seikowatches.com when we checked on 23 Oct 2026. Prices change, so check before you buy.
Will the Seiko SPB155 fit my wrist?
By our sizing guide it sits best on wrists of about 15.5–17.0 cm (6.1–6.7 in). Use the fit checker on this page to test your own wrist.
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