Seiko SPB121
Ref. SPB121 · In production
- Case39.5 mm
- Thick13.2 mm
- Water res.200 m
- MovementAutomatic
- CrystalSapphire
Overview
The Seiko SPB121 is a field watch from the Prospex collection, part of the Seiko Alpinist family. It has a 39.5 mm stainless steel case, 13.2 mm thick. Inside is a automatic movement (calibre 6R35) with 70 h of power reserve. You also get 200 m water resistance and a sapphire crystal.
Who it suits
- Wrists of roughly 15.7–17.7 cm (6.2–7.0 in), by our Watch Finder sizing guide
- Swimming, snorkelling and diving
Strengths
- Sapphire crystal resists scratches
- 200 m water resistance
- 70 h power reserve survives a weekend off the wrist
Written by Watch.co from the published specs below. These are not owner reviews.
Full specifications
Case
| Case diameter | 39.5 mm | seikowatches.com · 23 Oct 2026 |
|---|---|---|
| Thickness | 13.2 mm | seikowatches.com · 23 Oct 2026 |
| Case material | Stainless steel | seikowatches.com · 23 Oct 2026 |
| Crystal | Sapphire | seikowatches.com · 23 Oct 2026 |
| Water resistance | 200 m | seikowatches.com · 23 Oct 2026 |
Movement
| Movement type | Automatic | seikowatches.com · 23 Oct 2026 |
|---|---|---|
| Calibre | 6R35 | seikowatches.com · 23 Oct 2026 |
| Power reserve | 70 h | seikowatches.com · 23 Oct 2026 |
Strap / Bracelet
| 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) | Field | seikowatches.com · 23 Oct 2026 |
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 SPB121
How big is the Seiko SPB121?
The case is 39.5 mm wide, 13.2 mm thick.
What movement does the Seiko SPB121 use?
It uses the 6R35 calibre, a automatic movement with 70 h of power reserve.
Can I swim with the Seiko SPB121?
Yes. It is rated to 200 m.
How much is the Seiko SPB121?
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 SPB121 fit my wrist?
By our sizing guide it sits best on wrists of about 15.7–17.7 cm (6.2–7.0 in). Use the fit checker on this page to test your own wrist.
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