Identify a Seiko From a Photo: Model and Caseback Code Guide

Turn a Seiko over and you will find two things engraved on the caseback: a calibre-case code in the form 7S26-0020, and a serial number, usually six digits. You will also see the water resistance rating, the case material and often the country of manufacture. What you will not find is the model code. SKX007, SRPD55 and SPB143 are catalogue numbers that appear on the hang tag, the box label and the warranty card, not on the watch.

That is why one caseback code can cover several watches. The code describes the movement and case; the model code adds the dial, bezel and bracelet, so SKX007, SKX009 and SKX011 all read 7S26-0020 on the back.

Vintage Seikos follow the same system, with codes such as 6139-6002 on 1970s chronographs or 6309-7040 on the original Turtle divers. Many also carry a small factory symbol on the dial or caseback. For the cross-brand picture, see our guide to watch reference numbers.

The code before the hyphen is the calibre, the code after it is the case. In 7S26-0020, 7S26 is a 21-jewel automatic that neither hacks nor hand-winds, and 0020 is the SKX case. Knowing the calibre family tells you a lot about the watch's position in the range.

As a rule of thumb: 7S is the basic automatic, 4R adds hacking and hand-winding, 6R is the mid-range automatic with a longer power reserve, 8L is the high-grade automatic used in top Prospex divers, 9R is Spring Drive, 9S and 9F are Grand Seiko mechanical and quartz, V-series calibres are solar, 7T are quartz chronographs and 7N are basic quartz.

The serial on a Seiko caseback is usually six digits, and the first two tell you when the watch was made. The first digit is the last digit of the year and the second is the month, with 1 to 9 for January to September and the letters O, N and D for October, November and December. A serial beginning 8N was therefore made in November of a year ending in 8.

The system does not tell you the decade. A 7S26-0020 with a serial starting 8 could be from 1998, 2008 or 2018, because the SKX was produced across all three. Narrow it down with the calibre's production run, the dial text and the packaging. A 4R36 cannot be older than the early 2010s; a 6R35 cannot be older than 2019.

One further cue helps. A J at the end of the model code (SKX007J1) means the watch was assembled in Japan and the dial usually reads Made in Japan; a K means it was assembled elsewhere, often Malaysia.

• Seiko 5 and 5 Sports: the shield-shaped 5 logo on the dial, a day-date window at 3 and, on classic models, a crown at 4 o'clock and a display caseback. The 2019 5 Sports range borrowed the SKX case shape.
• Prospex: the X logo (the Prospex mark) on the dial since the mid-2010s, together with Diver's 200m or similar text. Divers, field watches and solar chronographs all sit here.
• Presage: dress watches with the Presage name on the dial and often a decorative dial finish, from pressed patterns to enamel and porcelain.
• Astron: GPS solar watches, usually large, with Astron on the dial.
• King Seiko and Grand Seiko: King Seiko returned in the 2020s with its own crest. Grand Seiko has been a separate brand since 2017, and dials made since then read only Grand Seiko, so a dial that also says Seiko is from before 2017.
• Vintage: Lord Matic, Bell-Matic, the 6139 and 6138 chronographs and the 6105 and 6309 divers, often with a Suwa whirl or Daini lightning-bolt symbol on the dial.

• SKX007 or 5 Sports SRPD: the cases are nearly identical. The SKX has no 5 shield, a screw-down crown, a 7S26 and Diver's 200m on the dial; the SRPD has the shield, a push-pull crown, a 4R36 and a 100 m rating.
• Seiko, Grand Seiko or King Seiko: separate lines with their own logos; Grand Seiko uses SBGA, SBGR and SBGX prefixes.
• Modded Seikos: the SKX, 5 Sports and Turtle are among the most commonly modified watches anywhere, with aftermarket dials, hands, bezels and crystals. The caseback code will still be genuine; the dial may not be.
• Franken vintage: old Seikos are often assembled from parts of several watches. Check that the dial code printed at 6 o'clock matches the caseback calibre.
• Dive-watch homages: the SKX and Turtle borrow cues from Swiss divers and are borrowed from in turn. See our Rolex and Omega guides for the originals.

Outright counterfeits exist, mostly of the SKX and of Grand Seiko, but misrepresented mods are the bigger risk. Our guide to spotting a fake luxury watch covers the general method.

Seiko is a brand where photo identification is especially useful, because the model code is not on the watch and the range is vast. WatchID matches the case shape, bezel, dial layout, hand set and logo against known Seiko models and returns candidates with their catalogue codes, so you can go from a wrist shot to SRPD55 or SPB143 without decoding anything.

1. Photograph the dial straight on, making sure the text lines at 6 o'clock are legible.
2. Photograph the caseback; the calibre-case code confirms or rules out the candidates.
3. If the watch is modified, expect the base model rather than the exact mod.
4. Match the caseback code to the candidate. A 7S26-0020 cannot be an SRPD, however similar it looks.

Limits: a photo cannot tell a J from a K version unless the dial text is readable, cannot confirm the movement, and can be fooled by well-made aftermarket dials. For the method in detail, read how to identify a watch from a photo; our guide to quartz versus automatic movements covers Seiko's two movement families.