Reference pages
Seiko Sumo
The enthusiast's mid-size Prospex diver: sapphire, 200m ISO, a 6R movement. Here is what it is and the in-production alternatives.
By Stephen V. · Updated Aug 8, 2026
The Sumo is a 45 mm Prospex diver — 200 m, ISO 6425, a sapphire crystal, and a 6R-series automatic — that sits between the entry Turtle and the higher Marinemaster divers. Current Sumo references (the SPB103 / SPB323 generation) exist but turn up inconsistently through mainstream retailers, so if a specific Sumo is not available, the in-production SPB117 and the Turtle are the honest alternatives.
What the Sumo is
The Sumo earned its following by being the Seiko diver that stopped compromising without reaching Marinemaster prices. It pairs a genuine 200 m ISO 6425 rating with a sapphire crystal — not the Hardlex of the Turtle and Samurai— and a 6R-series movement with a longer reserve than the 4R family. The name comes from the broad, planted case, which wears large.
It is a big watch. At 45 mm with the height a 200 m diver needs, it is not the one to reach for if a Turtle already feels like a lot on your wrist — the 39.5 mm SPB references exist for exactly that reason.
Availability, honestly
The Sumo is in Seiko’s current catalog, but the specific references move in and out of stock at mainstream retailers, and we will only point you at a watch we can confirm is buyable now. So rather than send you to a listing that may be gone, the two references below are the in-production divers we can stand behind today:
The SPB117gives you the same things that make the Sumo desirable — sapphire, 200 m ISO, the 70-hour 6R35 — in a more wearable 39.5 mm case. If the Sumo’s appeal is the specification rather than the size, this is the closer match.
The Turtleis the cheaper way into a 200 m ISO Seiko diver. It uses Hardlex rather than sapphire, but its cushion case wears more easily than the Sumo’s width suggests it should.
The watches on this page
Specifications are transcribed from Seiko’s published documentation. Prices come from Amazon and carry the date they were verified. We have not handled these watches — here is what we did instead.
No buyable offer at the last check (Sep 8, 2026). We show nothing rather than a stale number.
#ad · we may earn a commission from this link to Seiko Prospex SPB117
Seiko Prospex SPB117
SPB117J1Best for: The best-proportioned Seiko diver, if the budget stretches
The 62MAS-lineage diver: 39.5 mm, sapphire, and the 70-hour 6R35. This is where Seiko stops compromising, and the price step reflects it.
- Spec completeness for the price
- 9.3
- Movement relative to bracket
- 9.2
- Case proportions
- 9.6
- Strap flexibility
- 9.2
- Availability
- 7.9
What it gets right
- 70-hour power reserve — leave it off over a weekend and it is still running
- Sapphire, and a tighter stated accuracy spec than the 4R family
- 39.5 mm with a 46.4 mm lug-to-lug is the most universally wearable diver Seiko makes
What it gets wrong
- Roughly double the price of a Turtle
- 6R35 is still a 21,600 vph movement, so the seconds sweep is no smoother
- 20 mm lugs on a diver feel narrow to some
Skip this one if: your budget is doing other work. A Turtle is the same water rating and the same 6-beat sweep for half the money; what you buy here is sapphire, the power reserve and the proportions.
| Case diameter | 39.5 mm |
|---|---|
| Lug-to-lug | 46.4 mm |
| Thickness | 12.4 mm |
| Lug width | 20 mm |
| Crystal | Sapphire with anti-reflective coating |
| Water resistance | 200 m, ISO 6425 rated |
| Crown | Screw-down |
| Caliber | Seiko 6R35 |
| Type | Automatic, hand-winding and hacking |
| Beat rate | 21,600 vph (6 beats/sec) |
| Jewels | 24 |
| Power reserve | Approx. 70 hours |
| Stated accuracy | -15 to +25 sec/day |
| Complications | Date |
$550.0011% off
Price as of Sep 8, 2026. Prices move — Amazon's is the one that counts.
#ad · we may earn a commission from this link to Seiko Prospex Turtle SRPE99
Seiko Prospex Turtle SRPE99
SRPE99K1Best for: An actual dive watch you can also wear daily
A real 200 m ISO-rated diver with a screw-down crown, in the cushion case that wears far smaller than its 45 mm suggests.
- Spec completeness for the price
- 9.0
- Movement relative to bracket
- 8.5
- Case proportions
- 8.8
- Strap flexibility
- 9.5
- Availability
- 8.6
What it gets right
- Genuine ISO 6425 diver, not a diver-styled sports watch
- 47.7 mm lug-to-lug means it fits wrists that 45 mm suggests it should not
- Screw-down crown at 4 o'clock keeps it off the back of your hand
What it gets wrong
- Hardlex on a watch at this price is the recurring Seiko complaint
- The 45 mm figure scares people off before they try one
- PADI co-branding on the dial is not for everyone
Skip this one if: you have a wrist under about 6.5 inches. The lug-to-lug is forgiving but the case is still visually wide, and the smaller SRPG references exist for exactly this reason.
| Case diameter | 45.0 mm (cushion case) |
|---|---|
| Lug-to-lug | 47.7 mm |
| Thickness | 13.4 mm |
| Lug width | 22 mm |
| Crystal | Hardlex (hardened mineral) |
| Water resistance | 200 m, ISO 6425 rated for scuba diving |
| Crown | Screw-down, at 4 o'clock |
| Bezel | Unidirectional elapsed-timing bezel, PADI red and blue |
| Bracelet | Steel, three-fold clasp with push-button release |
| Caliber | Seiko 4R36 |
| Type | Automatic, hand-winding and hacking |
| Beat rate | 21,600 vph (6 beats/sec) |
| Jewels | 24 |
| Power reserve | Approx. 41 hours |
| Stated accuracy | -35 to +45 sec/day |
| Complications | Day and date |
Questions
Is the Seiko Sumo still made?
Yes, the current SPB103 / SPB323 generation is in Seiko’s catalog, but specific references move in and out of stock at mainstream retailers. If the one you want is unavailable, the SPB117 offers the same sapphire-and-6R specification in a smaller case.
How big is the Seiko Sumo?
About 45 mm, and it wears large — a planted, broad case. If that is too much, the 39.5 mm SPB divers give you the same 200 m sapphire specification in a more wearable size.
Does the Sumo have a sapphire crystal?
Yes — that is a large part of its appeal. It sits above the Hardlex-crystal Turtle and Samurai on that front, with a 6R-series movement rather than the 4R family.
Sumo or Turtle?
The Sumo adds sapphire, a 6R movement and more presence; the Turtle is cheaper, uses Hardlex and wears more easily. If the budget stretches and you want the bigger, better- finished diver, the Sumo; if value and wearability lead, the Turtle.
Sources
- Seiko Prospex collection — official specifications
- ISO 6425 — Horology, divers' watches (standard listing)
- Seiko Watch Corporation — US catalog and specifications
- Seiko instruction manuals and caliber documentation
Specifications are transcribed from manufacturer documentation and published standards. Where a manufacturer does not publish a figure, this page says so rather than estimating one.