Seiko Prospex SPB143 vs SPB185: Which Dive Watch Is Worth Owning

Seiko's modern Prospex collection has filled the sub-$2,000 mechanical dive watch category with specific confidence over the past five years. The SPB143 (launched 2020) and SPB185 (launched 2022) represent the best current options in this price range, and for most buyers considering a dive watch below $2,500 retail, one of these two references is the correct answer. Swiss alternatives at this price — the Tissot Seastar, the Longines HydroConquest, the Oris Divers Sixty-Five — don't match the Seiko's combination of in-house movement, finishing quality, and design maturity.

I've owned the SPB143 for three years. My brother owns the SPB185. We compare them directly when we meet up, and after extended comparison, my conclusion is that the SPB143 is the better choice for most buyers — specifically because its design language is more distinctive and its wearing experience is slightly more refined. The SPB185 is objectively a strong watch, but it reads slightly more generic and doesn't offer specific advantages that justify its $400 price premium over the SPB143. Here's the detailed comparison.

The SPB143 Reference

Launched 2020 as part of Seiko's 140th anniversary collection, the SPB143 is a 40.5mm × 13.2mm stainless steel dive watch with a black dial featuring applied indices, a black aluminum bezel insert, and Seiko's 6R35 automatic movement. Retail price is $1,400 in April 2026, though street pricing through Seiko authorized dealers frequently runs $1,100-$1,250.

The reference is an homage to the 1965 Seiko 62MAS, Seiko's first dive watch and a historically significant reference in watchmaking. The case proportions, dial layout, and hand design all derive from the 62MAS with modern execution. This homage positioning is explicit — Seiko actively markets the SPB143 as a reinterpretation of the 62MAS, and the design decisions reflect that intent.

• Case 40.5mm × 13.2mm, stainless steel
• Calibre 6R35 automatic, 70-hour reserve
• Sapphire crystal with anti-reflective coating
• 200m water resistance, screw-down crown

The calibre 6R35 is Seiko's current mid-tier automatic movement. 21,600 bph, 70-hour power reserve, 24 jewels, hacking seconds and manual winding support. Accuracy is specified at -15/+25 seconds per day — significantly less tight than Swiss chronometer grade. In practice, properly regulated 6R35 movements often run at -5/+10 seconds per day, which is acceptable for daily wear but not exceptional.

The SPB185 Reference

Launched 2022 as a successor to the earlier SPB051 and SPB053 references, the SPB185 is a 41mm × 13.2mm case with a black dial, steel bezel with raised numeral markers, and the same 6R35 movement as the SPB143. Retail is $1,800, typical street pricing $1,500-$1,700.

The SPB185 references Seiko's 1968 diver references more than the 62MAS that influenced the SPB143. Different case geometry (slightly more squared lug profile), different bezel treatment (raised polished numerals rather than painted ones on aluminum), and different dial execution (Seiko's "Prospex Glow" treatment with enhanced luminous intensity). These are meaningful differences but subtle enough that direct comparison is required to evaluate them.

The SPB185's raised bezel numerals are the most visually distinctive feature. Each hour marker on the bezel is a separate raised polished steel element rather than a printed graphic. This creates depth and visual interest that the SPB143's flat bezel doesn't have. Whether this is worth the $400 price premium depends on specific aesthetic preference.

Direct Comparison

Case dimensions. SPB143 is 40.5mm × 13.2mm; SPB185 is 41mm × 13.2mm. Half millimeter difference in diameter is barely perceptible, but the SPB185's slightly different lug geometry makes it wear ever so slightly larger. For wrists below 7 inches, the SPB143 is marginally more appropriate. For wrists above 7.25 inches, the SPB185 fits slightly better.

Dial design. SPB143 dial reads cleaner and more vintage-inspired. Large applied rectangular indices, leaf-shaped hour and minute hands, simple "Prospex X" logo at 6 o'clock. SPB185 dial is similar but slightly busier — "Prospex" text at 6 and additional date window detailing. Both are legible; SPB143 has the minor advantage for pure aesthetic purity.

Bezel. SPB143 has a black aluminum insert with white printed numerals. SPB185 has a steel bezel with raised polished numerals. The SPB185's bezel is objectively more refined and more expensive to manufacture. The SPB143's aluminum bezel has a specific charm — it's closer to the original 1965 62MAS execution and ages more gracefully as the aluminum develops subtle patina over years of wear.

Hands. SPB143 has leaf-style hour and minute hands derived from 1960s Seiko aesthetic. SPB185 has more modern dart-style hands. Neither is objectively better; both work for their respective references. For buyers who prefer vintage-inspired hand styles, SPB143 is correct. For more modern sport-watch aesthetic, SPB185 works.

The Movement Consideration

Both watches use the identical calibre 6R35 movement. This means accuracy performance, power reserve, mechanical feel, and service considerations are identical across both references. Any movement-based argument for one reference over the other is invalid — they're mechanically the same watch.

This is worth emphasizing because some buyers assume the more expensive SPB185 has a superior movement. It doesn't. The price difference between SPB143 and SPB185 reflects case and dial differences, not movement upgrades. If movement specifications are your primary concern, both watches offer identical value at this level.

For buyers willing to step up to Seiko's higher-tier movements: the 6R65 series (used in some Grand Seiko-adjacent Prospex references at $2,500-$3,500) offers improved accuracy specs and longer power reserves. The Spring Drive 9R65 calibre (used in Grand Seiko references at $4,500+) offers dramatically superior accuracy (±1 second per day) and the distinctive glide motion seconds hand. Moving up the Seiko movement hierarchy requires corresponding price increases but delivers meaningfully better mechanical performance.

Strap and Bracelet Options

Both references ship with stainless steel bracelets in addition to being available on rubber and leather straps. The factory bracelets are functional but not exceptional — three-link brushed finish, standard pin-and-collar link removal, pressure-fit clasp that works but isn't as refined as higher-tier references.

The bracelets are the weakest element of both watches. Aftermarket options from Uncle Seiko, Strapcode, or Crafter Blue offer meaningful upgrades for $60-$180. A beads-of-rice aftermarket bracelet on either SPB143 or SPB185 transforms the watch's formality range — the factory bracelets limit both watches to sport-casual wear, while refined aftermarket options enable dress-adjacent wear.

For rubber strap usage, both watches work well with aftermarket offerings. The Erika's Originals Diver Strap, Crafter Blue CB07, and Uncle Seiko Waffle Strap are all compatible and genuinely improve the watches' sport and active-wear versatility. Budget for one aftermarket rubber strap ($80-$150) within the first year of ownership.

The Verdict

The SPB143 is the better buy for most collectors. Specific reasons: it's $400 less, the 62MAS-inspired design is more distinctive than generic 1968 diver styling, the aluminum bezel has character that the steel bezel lacks, and the leaf-style hands are aesthetically purer than the SPB185's dart hands. For a first mechanical dive watch or an addition to an existing collection where you want vintage-inspired Seiko diving heritage, the SPB143 is correct.

The SPB185 is the better buy for specific preferences: buyers who prefer steel bezel with raised numerals over aluminum printed numerals, buyers who want slightly larger case dimensions, and buyers who prefer more modern hand styles over vintage leaf-shape hands. The $400 premium is justified if these specific preferences align with what you want.

For collectors evaluating both against Swiss alternatives in the $1,500-$2,500 range: the Seikos offer better value per dollar than most Swiss options. The Tissot Seastar at similar price offers Swiss manufacturing but weaker in-house movement (ETA-derived Powermatic 80 vs Seiko's 6R35). The Oris Divers Sixty-Five at $2,200+ offers SW200-based movements with shorter power reserves. The Longines HydroConquest at $1,750 offers reliable but generic design. The Seikos win the value comparison in this price band for serious mechanical specifications per dollar spent.

For buyers willing to step up to $4,000, the Tudor Black Bay 58 is the correct choice — it's mechanically superior to both Seiko references, offers Swiss manufacturing at higher finishing standards, and has better secondary market value retention. But at its price point, the SPB143 is unbeatable for what you get in mechanical dive watch ownership. This is the right first serious watch for many collectors, and for some, it's the only watch they ever end up needing.