Hamilton Khaki Field Auto vs Seiko Alpinist
Hamilton Khaki Field Auto H70455533 vs Seiko SPB121, compared on the specs each brand publishes.
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The short answer
Two field-style automatics, compared on Hamilton's and Seiko's specs.
- Case size: the Seiko SPB121 is 1.5 mm larger (39.5 mm vs 38 mm).
- Thickness: the Seiko SPB121 is 2.2 mm thicker (13.2 mm vs 11 mm).
- Water resistance: the Seiko SPB121 is 100 m more (200 m vs 100 m).
- Power reserve: the Hamilton Khaki Field Auto H70455533 is 10 hours longer (80 h vs 70 h).
- Price: the Seiko SPB121 lists for $70 less in the US ($725 vs $795).
Side-by-side specs
| Spec | Hamilton Khaki Field Auto H70455533 | Seiko SPB121 |
|---|---|---|
| Case diameter | 38 mm | 39.5 mm |
| Thickness | 11 mm | 13.2 mm |
| Lug width | 20 mm | 20 mm |
| Calibre | H-10 | 6R35 |
| Movement | Automatic | Automatic |
| Power reserve | 80 h | 70 h |
| Water resistance | 100 m | 200 m |
| Crystal | Sapphire | Sapphire |
| Case material | Stainless steel | Stainless steel |
| Ships on | Leather strap | Not stated |
| US list price | $795 (US list) | $725 (US list) |
| Dial | Black | Not stated |
| Status | In production | In production |
| Suits wrists of about our sizing guide | 15.1–17.0 cm | 15.7–17.7 cm |
Specs summarised in our own words from the brand's product pages: H70455533 source (checked 3 Nov 2026) SPB121 source (checked 23 Oct 2026). "Not published" means the brand page we checked doesn't list it, so we leave it blank rather than guess.
All the differences
- Case size: the Seiko SPB121 is 1.5 mm larger (39.5 mm vs 38 mm).
- Thickness: the Seiko SPB121 is 2.2 mm thicker (13.2 mm vs 11 mm).
- Water resistance: the Seiko SPB121 is 100 m more (200 m vs 100 m).
- Power reserve: the Hamilton Khaki Field Auto H70455533 is 10 hours longer (80 h vs 70 h).
- Price: the Seiko SPB121 lists for $70 less in the US ($725 vs $795).
- Calibre: Hamilton Khaki Field Auto H70455533 has H-10; Seiko SPB121 has 6R35.
Wrist fit
Lug-to-lug decides overhang more than diameter does. Enter your wrist to see how each one should wear.
- Hamilton Khaki Field Auto H70455533 –
- Seiko SPB121 –
Same rule of thumb as Watch Finder: case diameter of about 23.5% of your wrist circumference (−2 mm to +2.5 mm), and lug-to-lug no longer than about 29% of it plus 1 mm. A guide, not a rule; flat or round wrists differ.
Strap fit
Both take 20 mm straps, so straps move between them. Size charts: Hamilton lug width chart · lug width chart.
Which should you buy?
It is the more compact case on paper (38 mm across). Our sizing guide puts it at about 15.1–17.0 cm.
It has the lower US list price, $725, a $70 difference.
It has the higher water-resistance rating: 200 m vs 100 m.
It is the slimmer case at 11 mm.
It has the longer published power reserve: 80 h.
Prices and where to buy
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More: All Hamilton Khaki Field references · All Seiko Prospex references.
Questions
Which is bigger, the Hamilton Khaki Field Auto H70455533 or the Seiko SPB121?
Per the brands, the Hamilton Khaki Field Auto H70455533 is 38 mm across and the Seiko SPB121 is 39.5 mm.
Which is cheaper?
The Seiko SPB121, at a US list price of $725 vs $795 when we checked.
Which is more water-resistant?
Hamilton Khaki Field Auto H70455533: 100 m. Seiko SPB121: 200 m.
Have you tested these watches?
No. This comparison uses brand-published specs and our own analysis of them, not hands-on testing.
Watch.co is independent and not affiliated with any brand. We haven't handled these watches for this page: everything here comes from brand-published specs and our own analysis. Brand names are used only to identify products.