Side-by-side comparison of specifications and features
Compare visual case presence and physical footprint on one shared wrist. Measure your top-down wrist width for a stronger result; lug-to-lug is used when the catalog has it.
Medium (6.7″)
Estimated top width: 56.7 mm
Preliminary range: 54.7–61.8 mm.
Watch A
Visual presence
ModerateCase covers 67% of your modeled wrist width.
Physical footprint
Clear spaceEstimated clearance: 4.8 mm per side.
Watch B
Visual presence
ModerateCase covers 67% of your modeled wrist width.
Physical footprint
Clear spaceEstimated clearance: 5.3 mm per side.
Proportional guide only: visual presence and physical footprint do not predict comfort. Weight, thickness, caseback shape, rigid lugs, strap stiffness, wrist-bone prominence, wearing tension, bezel design, and case curvature change how a watch actually wears.
Start with the specifications that meaningfully differ. Expand the complete table for reference details and missing-data context.
| Specification | Hamilton Khaki Field Auto | Seiko Prospex |
|---|---|---|
| Pricing | ||
| MSRPKhaki Field Auto is $30 less at MSRP | $695 | $725 |
| New PriceProspex is $176.1 less based on the current snapshot | $710 | $534 |
| Used Price (Low)Prospex is $298.9 less at the low end | $599 | $300 |
| Used Price (High) | $649 | $3,750 |
| 30-Day Trend | ↑ +0.9% | ↓ -19.7% |
| Used Price Range | $599 - $649 | $300 - $3,750 |
| Identity | ||
| Style | Field, Tool | Field, Sports, Tool |
| Dimensions | ||
| ThicknessKhaki Field Auto is 1.9mm thinner | 11mm | 12.9mm |
| WeightKhaki Field Auto is 75g lighter | 69g | 144g |
| Lug to Lug | 47mm | 46mm |
| Case | ||
| Water ResistanceProspex adds 100m water resistance | 100m (recreational diving) | 200m (diving) |
| Dial | ||
| Dial Color | Black | Green |
If you are deciding between Hamilton Khaki Field Auto and Seiko Prospex SPB155 (Baby Alpinist), the real decision is usually about water-ready utility versus dressier everyday wear. They both touch the field and tool use case, so smaller spec differences can matter more than brand preference.
Bottom line
Water resistance is a meaningful separator here — the higher-rated option gives more flexibility for swimming or rougher daily use. Choose Hamilton Khaki Field Auto if you want the lighter watch (69g vs 144g); choose Seiko Prospex SPB155 (Baby Alpinist) when swimming, beach use, or tougher daily wear is part of the plan.
Choose Hamilton Khaki Field Auto when
Hamilton Khaki Field Auto is a better fit for mechanical-watch enthusiasts, field styling.
Choose Seiko Prospex SPB155 (Baby Alpinist) when
Seiko Prospex SPB155 (Baby Alpinist) is a better fit for mechanical-watch enthusiasts, field styling.
Movement and upkeep
Hamilton Khaki Field Auto: automatic movement
Seiko Prospex SPB155 (Baby Alpinist): automatic movement
Both use the same movement type, so maintenance differences are limited and fit or feature details should decide the purchase.
Size and wearability
Hamilton Khaki Field Auto: 38mm · L2L 47mm · 69g
Seiko Prospex SPB155 (Baby Alpinist): 38mm · L2L 46mm · 144g
Their size profiles are relatively close, so fit comes down to shape, weight, and how each watch sits on your wrist.
Water resistance
Hamilton Khaki Field Auto: 100m
Seiko Prospex SPB155 (Baby Alpinist): 200m
Water resistance is a meaningful separator here — the higher-rated option gives more flexibility for swimming or rougher daily use.
Price and value
Hamilton Khaki Field Auto: $620
Seiko Prospex SPB155 (Baby Alpinist): $534
These two often land in a similar price band — which usually means fit, features, and current deal quality matter more than the sticker price.
Style and use case
Hamilton Khaki Field Auto: field
Seiko Prospex SPB155 (Baby Alpinist): field
Both lean into a similar field use case — the choice is more about fit, features, and price than category.
Crystal and materials
Hamilton Khaki Field Auto: sapphire crystal · steel
Seiko Prospex SPB155 (Baby Alpinist): sapphire crystal · steel
Materials are broadly similar, so finish, fit, and price will matter more than the materials list alone.
Seiko Prospex SPB155 (Baby Alpinist) usually offers the lower entry price — confirm current listings because marketplace pricing can move quickly.
These two often land in a similar price band — which usually means fit, features, and current deal quality matter more than the sticker price.
Check current deals on Amazon and eBay using the buttons below — listing prices, seller quality, and condition can change quickly.
Prices change often, so compare the latest listings and condition options before you buy.
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Hamilton Khaki Field Auto
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Seiko Prospex
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Seiko Prospex SPB155 (Baby Alpinist) — it is 46mm lug-to-lug versus 47mm, and lug-to-lug is what decides whether a watch overhangs a smaller wrist.
Seiko Prospex SPB155 (Baby Alpinist) — it is rated 200m versus 100m. Both are in the same broad bracket, so treat this as a tiebreaker rather than a deciding factor.
Seiko Prospex SPB155 (Baby Alpinist) is the value pick at roughly $86 less. Pay more only if a specific difference above matters to you — otherwise the cheaper one is the smarter buy. Confirm live listings, since marketplace pricing moves.
Evidence & Method
This page currently relies on normalized catalog fields and calculated differences. No external reviewer observation is used in its verdict.
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