Hamilton Khaki Field Automatic vs Seiko 5 Sports
Same 100m rating, roughly triple the price
Quick Verdict
The Hamilton Khaki Field Automatic ($500–$1,000) and the Seiko 5 Sports ($250–$500) are both 100m-rated automatics aimed at the same everyday job. The Hamilton adds a sapphire crystal, an 80-hour power reserve and a more wearable 38mm case. The Seiko costs roughly a third as much and adds a day to the date.
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Specifications Compared
| Feature | Hamilton Khaki Field Automatic | Seiko 5 Sports 5KX |
|---|---|---|
| Price | $500–$1,000 | $250–$500 |
| Case Size | 38mm | 42.5mm |
| Movement | Automatic H-10 | Automatic Caliber 4R36 |
| Caliber Type | Automatic (ETA C07.611 base) | Seiko In-House Automatic |
| Power Reserve | 80 Hours | 41 Hours |
| Water Resistance | 100m (10 ATM) | 100m (10 ATM) |
| Crystal | Sapphire Crystal | Hardlex Crystal |
| Case Material | Stainless Steel | Stainless Steel |
| Origin | Swiss Made | Made in Japan |
Category-by-Category Analysis
Design & Aesthetics
Field-watch discipline against sports-watch practicality
The Khaki Field Automatic is a proper field watch — legible, restrained, with a 24-hour inner ring and a date. The Seiko 5 Sports is a sports watch with a rotating bezel and a day-date window. The Hamilton is the more disciplined design; the Seiko gives you more to work with on the dial.
Movement & Performance
Eighty hours against forty-one
The Hamilton runs the H-10, based on the ETA C07.611, with an 80-hour power reserve. The Seiko runs the in-house 4R36 with 41 hours and a day-date. The reserve gap is the practical one: leave the Hamilton off on Friday evening and it is still running Monday morning, where the Seiko will have stopped. The 4R36 answers by being one of the most widely serviced movements anywhere.
Wearability & Fit
The Hamilton is the more versatile size
At 38mm the Khaki Field Automatic suits a far wider range of wrists than the 42.5mm Seiko 5 Sports, and it is the easier of the two to wear under a sleeve. Both are stainless steel and both are rated to 100m, so the fit is where this is decided rather than the build.
Value & Cost of Ownership
The Seiko delivers the same water rating for a third of the price
The Seiko sits in the $250–$500 band and the Hamilton in $500–$1,000, and the headline capability — a 100m-rated mechanical automatic — is identical. The Hamilton premium buys sapphire, nearly double the power reserve, Swiss manufacture and a smaller case. Both are sensible purchases; only one of them is the obvious value pick.
Brand Heritage
Military lineage against the default first automatic
Hamilton supplied field watches to the U.S. military and the Khaki Field line descends directly from that. Seiko 5 has been the standard answer to "what should my first mechanical watch be" for decades. Both have earned their reputations, and neither is coasting on them.
Our Verdict
Hamilton
Khaki Field Automatic
Choose the Hamilton if you want the better-made version of the same idea. Sapphire instead of Hardlex, 80 hours of reserve instead of 41, Swiss Made, and 38mm rather than 42.5mm. It is the watch you keep, and it costs a band more for good reasons.
Check Price on AmazonSeiko
5 Sports 5KX
Choose the Seiko 5 Sports if the value is the point. You get the same 100m rating and a genuine automatic with a day-date for roughly a third of the price. Hardlex will scratch where sapphire would not, and 41 hours means it stops over a weekend off the wrist, but nothing else at this money does the job as well.
Check Price on AmazonThe Bottom Line
The Hamilton Khaki Field Automatic and the Seiko 5 Sports SRPD55 are both automatic watches rated to 100m, but the Hamilton has a sapphire crystal and an 80-hour power reserve in a 38mm case, while the Seiko uses Hardlex with a 41-hour reserve in a 42.5mm case.
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How This Page Was Made
Our comparisons are generated from a hand-maintained specification database and reviewed under our editorial standards. We use AI tools to assemble pages from that data. We don’t invent specs: every number traces back to the database, and when we correct an entry, the fix is applied site-wide. As an Amazon Associate, The Horologist earns from qualifying purchases.