Seiko HDB012J8
Ref. HDB012J8 · In production
- Case42.5 mm
- Thick13.4 mm
- Lug-to-lug46 mm
- Water res.100 m
- MovementAutomatic
- CrystalHardlex (mineral)
Overview
The Seiko HDB012J8 is a sports watch from the Seiko 5 Sports collection. It has a 42.5 mm stainless steel case, 13.4 mm thick, 46 mm from lug to lug. Inside is a automatic movement (calibre 4R36) with 41 h of power reserve. You also get 100 m water resistance, a hardlex (mineral) crystal and a bracelet.
Who it suits
- Wrists of roughly 17.0–18.9 cm (6.7–7.5 in), by our Watch Finder sizing guide
- Everyday wear including swimming
- People who enjoy seeing a mechanical movement at work
Strengths
- Compact 46 mm lug-to-lug suits smaller wrists
- Display caseback shows the movement
- Hacks and hand-winds, so it is easy to set
Trade-offs
- Hardlex (mineral) crystal scratches more easily than sapphire
- 41 h power reserve: it stops after about a day and a half off the wrist
- Limited edition: may be hard to find new
Written by Watch.co from the published specs below. These are not owner reviews.
Full specifications
Case
| Case diameter | 42.5 mm | seikowatches.com · 23 Oct 2026 |
|---|---|---|
| Thickness | 13.4 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 | Hardlex (mineral) | seikowatches.com · 23 Oct 2026 |
| Caseback | Display (see-through) | seikowatches.com · 23 Oct 2026 |
| Bezel | Unidirectional rotating | seikowatches.com · 23 Oct 2026 |
| Water resistance | 100 m | seikowatches.com · 23 Oct 2026 |
| Magnetic resistance | 4,800 A/m | seikowatches.com · 23 Oct 2026 |
Dial
| Luminous material | LumiBrite | seikowatches.com · 23 Oct 2026 |
|---|---|---|
| Date | Day/Date | our classification |
Movement
| Movement type | Automatic | seikowatches.com · 23 Oct 2026 |
|---|---|---|
| Calibre | 4R36 | seikowatches.com · 23 Oct 2026 |
| Made in-house | Yes | seikowatches.com · 23 Oct 2026 |
| Power reserve | 41 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 | 22 mm | seikowatches.com · 23 Oct 2026 |
Other
| Production status | In production | seikowatches.com · 23 Oct 2026 |
|---|---|---|
| Limited edition | Yes | seikowatches.com · 23 Oct 2026 |
| Style (our classification) | Sports | 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.
Variants with the same specs
Same case, movement and bracelet or strap; typically a different dial or finish.
More in Seiko 5 Sports
Similar alternatives
Picked with Watch Finder's style tags and sizing.
Questions about the Seiko HDB012J8
How big is the Seiko HDB012J8?
The case is 42.5 mm wide, 13.4 mm thick and 46 mm from lug to lug.
What movement does the Seiko HDB012J8 use?
It uses the 4R36 calibre, a automatic movement with 41 h of power reserve.
Can I swim with the Seiko HDB012J8?
Yes. It is rated to 100 m.
Does the Seiko HDB012J8 have a date?
Yes, it shows the day and date.
Will the Seiko HDB012J8 fit my wrist?
By our sizing guide it sits best on wrists of about 17.0–18.9 cm (6.7–7.5 in). Use the fit checker on this page to test your own wrist.
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