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: 5.3 mm per side.
Watch B
Visual presence
BoldCase covers 69% of your modeled wrist width.
Physical footprint
Clear spaceEstimated clearance: 5.6 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 | Seiko Prospex | Seiko Prospex Speedtimer |
|---|---|---|
| Pricing | ||
| New PriceProspex is $369.5 less based on the current snapshot | $529 | $899 |
| Used Price (Low)Prospex is $228.4 less at the low end | $300 | $528 |
| Used Price (High) | $4,470 | $1,297 |
| 30-Day Trend | ↑ +4.3% | ↑ +3.3% |
| Used Price Range | $300 - $4,470 | $528 - $1,297 |
| Identity | ||
| Style | Field, Sports, Tool | Chronograph, Sports |
| Dimensions | ||
| DiameterProspex is 1mm smaller | 38mm | 39mm |
| ThicknessProspex is 0.8mm thinner | 12.9mm | 13.7mm |
| Lug to Lug | 46mm | 45.5mm |
| Movement | ||
| Movement | Automatic | Solar Powered |
| Case | ||
| Water ResistanceProspex adds 100m water resistance | 200m (diving) | 100m (recreational diving) |
| Bezel | Fixed | Tachymeter |
| Dial | ||
| Dial Color | Green | White |
1 field is excluded from the differences view because one watch lacks comparable data. Use “All specs” to inspect those gaps.
This Seiko Prospex SPB155 (Baby Alpinist) vs Seiko Prospex Speedtimer comparison is less about a universal winner and more about mechanical feel versus low-maintenance convenience, water-ready utility versus dressier everyday wear, field character versus chronograph versatility. They both touch the sports 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 Seiko Prospex SPB155 (Baby Alpinist) if you prefer a mechanical watch experience and do not mind more upkeep; choose Seiko Prospex Speedtimer if you want a lower-maintenance daily watch.
Choose Seiko Prospex SPB155 (Baby Alpinist) when
Seiko Prospex SPB155 (Baby Alpinist) is a better fit for mechanical-watch enthusiasts, field styling.
Choose Seiko Prospex Speedtimer when
Seiko Prospex Speedtimer is a better fit for low-maintenance daily wear, chronograph styling.
Movement and upkeep
Seiko Prospex SPB155 (Baby Alpinist): automatic movement
Seiko Prospex Speedtimer: solar movement
Seiko Prospex SPB155 (Baby Alpinist) uses a automatic movement, while Seiko Prospex Speedtimer uses a solar movement — that changes day-to-day ownership, upkeep, and the overall feel on the wrist.
Size and wearability
Seiko Prospex SPB155 (Baby Alpinist): 38mm · L2L 46mm · 144g
Seiko Prospex Speedtimer: 39mm · L2L 45.5mm
Their size profiles are relatively close, so fit comes down to shape, weight, and how each watch sits on your wrist.
Water resistance
Seiko Prospex SPB155 (Baby Alpinist): 200m
Seiko Prospex Speedtimer: 100m
Water resistance is a meaningful separator here — the higher-rated option gives more flexibility for swimming or rougher daily use.
Price and value
Seiko Prospex SPB155 (Baby Alpinist): $529
Seiko Prospex Speedtimer: $600
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
Seiko Prospex SPB155 (Baby Alpinist): field
Seiko Prospex Speedtimer: chronograph
Seiko Prospex SPB155 (Baby Alpinist) leans more field, while Seiko Prospex Speedtimer pulls toward chronograph use case — pick the one that matches how you will actually wear it.
Crystal and materials
Seiko Prospex SPB155 (Baby Alpinist): sapphire crystal · steel
Seiko Prospex Speedtimer: 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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Seiko Prospex
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Seiko Prospex Speedtimer
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Quartz and solar models are usually easier for grab-and-go use, while automatic and manual watches appeal more to buyers who enjoy the mechanical side of watch ownership.
Neither is clearly smaller: case width is 38mm vs 39mm and thickness 12.9mm vs 13.7mm. Pick on strap and looks instead — the size difference is not what will decide this for you.
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 $71 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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