Buying a watch online without being able to try it on is every enthusiast's fear. Too big, and the watch overhangs the wrist. Too small, and it disappears under the sleeve. With a hand-assembled Seiko Mod, this choice matters even more: each watch is made to order, shipped after a workshop test, and carries a personal signature.
Good news: finding the ideal size is no rocket science. In our French workshop, we have assembled and shipped more than 500 watches to date, and our customers have left us 50 reviews published on the site with an average rating of 5 out of 5 stars. We have gathered here everything we explain to every new customer: how to measure your wrist, which diameter to choose, and why diameter is only part of the equation. After six minutes of reading, you will know exactly which Seiko Mod size to order, and you will avoid the classic mistake of "I went bigger because it felt safer".
1. How to measure your wrist correctly (in 30 seconds)
Before talking diameter, you need reliable data: your wrist circumference, in centimetres.
The most accurate method remains a tailor's tape, laid flat just above the wrist bone, where you naturally wear a watch. Not higher up the forearm (the measurement would be wrong, the wrist widens), not lower on the hand. If you do not have a soft tape, a simple cord or piece of string does the job: wrap it around, mark the overlap point with a pen, then measure the resulting length with a ruler.
Two workshop tips:
- Take the measurement at the end of the day. The wrist swells slightly over the hours (heat, hydration, activity). The evening measurement better reflects the real wearing size, especially in summer.
- Measure twice. Once slightly tight, once completely loose. Take the average. That average corresponds to optimal wearing comfort.
For reference: the average adult wrist is 17 cm for men and 15.5 cm for women. If you are far from these values, do not panic, we have Seiko Mods suited to every profile.
2. Correspondence table: wrist circumference and Seiko Mod diameter
Here is the table we use in the workshop to guide new customers. It applies to a "classic" Seiko Mod (Datejust, Submariner, Nautilus, Royal Oak, Daytona, GMT), meaning the standard round format, not a cushion case or an XL pilot case.
| Wrist circumference | Ideal case diameter | Recommended Seiko Mod models |
|---|---|---|
| Under 15 cm | 36 mm | Ladies' Datejust, Datejust Arabic Ice Blue, Ladies' Datejust Rose |
| 15 to 16 cm | 36 to 39 mm | Datejust (Silver Diamond, Blue Diamond), Sky 39 mm configurator |
| 16 to 18 cm | 39 to 40 mm | SeikoMariner Pepsi, Nautilus, Daytona, Royal Oak Arabic White |
| 18 to 19 cm | 40 to 41 mm | SeikoMariner, GMT Blue, Nautilus, Daytona |
| Over 19 cm | 41 mm and up | GMT Blue or White, SeikoMariner on a wide oyster bracelet |
Important: these ranges are a starting point, not an absolute rule. A flat, wide wrist "wears" differently from a round, thin wrist at the same measurement. And some people prefer a slightly more present watch, or on the contrary a more discreet one. We come back to this just below.
3. Diameter is not everything: 3 other parameters to check
This is the most common mistake: focusing only on the millimetres shown on the product page. Three other measurements matter at least as much.
Lug-to-lug
Lug-to-lug is the length of the case measured from one lug to the other, from one strap attachment point to the opposite one. It is the figure that tells you whether the watch will "overhang" your wrist or not. For a 40 mm Submariner-style Seiko Mod, expect around 47 to 48 mm lug-to-lug. On a flat 17 cm wrist, it is perfect. On a round 15 cm wrist, it may start to overhang.
Rule of thumb: the lug-to-lug value in mm should not exceed the width of your wrist (measured flat, not the circumference) expressed in mm.
Case thickness
Our Seiko Mods sit around 12 to 13 mm thick, sometimes 14 mm for dive models. That is slim enough to slide under a shirt sleeve (the comfortable limit is around 14 mm). If you wear a suit every day, check this point: a watch that is too thick will catch on the cuff.
Strap width
It follows the case diameter:
- 18 mm for the 36 mm Datejust: elegant, discreet
- 20 mm for the 40 mm Submariner, Nautilus, Royal Oak, Daytona: the most versatile width
- 22 mm for the 41 mm GMT: a confident sporty presence
This width also determines your future options for alternative straps (leather, NATO, oyster, jubilee). If you change straps often, 20 mm gives you the widest choice on the market.
4. Which size for whom? The 4 cases we see most in the workshop
Case 1: Thin wrist, first elegant purchase
Wrist under 16 cm, looking for a dress watch for the office or evenings out. The 36 mm Datejust is the obvious choice. The Datejust Arabic Ice Blue (our best-seller) ticks every box: 36 mm, a detailed dial, a jubilee bracelet that hugs thin wrists perfectly. For a more feminine profile or a gift, the Ladies' Datejust (rose, gold, diamond) remains unbeatable.
Case 2: Medium wrist, everyday versatility
Between 16 and 18 cm: by far the most common range among our customers. 40 mm is the sweet spot: present enough for a sporty look, restrained enough for a meeting. The SeikoMariner Pepsi 40 mm is our reference in this format, a watch you can wear with a shirt, a t-shirt or a suit, with exactly the same effect. The blue Nautilus plays in the same register on the integrated-case side.
Case 3: Wide wrist, confident presence
Above 18 cm, you can (and should) move up to 41 mm. The GMT Blue and the GMT White have the advantage of a 22 mm bracelet that visually balances the case. A 40 mm Submariner on a wide oyster bracelet also works very well on square wrists.
Case 4: A gift, recipient's size unknown
With no information about the recipient's wrist, two safe options. Either you go for 40 mm (the "one size fits most" diameter that suits 80% of adult wrists), or you give a configurator: the recipient chooses their own case, dial and strap. Our five configurators, Submariner, Nautilus, Royal Oak, Daytona, Sky, cover the 36, 39, 40 and 41 mm diameters. You cannot go wrong.
5. FAQ: the 5 questions we get asked most in the workshop
Is a 40 mm Seiko Mod too big for a 15.5 cm wrist?
Not necessarily. On a flat, angular wrist, a 40 mm works very well thanks to a reasonable lug-to-lug (47 mm). On a round, domed wrist however, the 40 mm may visually overhang. If in doubt, go for 36-39 mm; a quick mirror test with a paper disc at the right diameter settles it in two seconds.
For women: do you have to go with 36 mm?
No, that is a stubborn cliché. Many of our female customers wear 40 mm with great success (on a 16-17 cm wrist it is perfect), especially on sporty models like the Submariner or GMT. The 36 mm remains more classic and elegant, but the choice depends on style, not gender.
How do I know if a watch is too small for me?
Three signs: the strap "disappears" between your wrist bones, the case seems to float in the middle of the wrist, or you feel like you are wearing a child's watch. A well-sized watch occupies about 50 to 60% of the visible width of the wrist when you look at your hand from above.
Can the bracelet of a Seiko Mod be shortened?
Yes, and it is included with shipping. We adjust every steel bracelet (oyster, jubilee, president) to your exact wrist size; just mention it in the order comments or by email at confirmation. No need to tinker on delivery. And if after a few weeks you need a link added or removed, our after-sales service takes care of it.
If I am unsure, which model should I go for first?
The SeikoMariner Pepsi 40 mm. It is our most versatile model, fits 80% of adult wrists, dresses up or down (shirt sleeve or t-shirt), and holds solid value on the second-hand market if you feel like upgrading in two years.
6. Choosing the right size without mistakes: that is what we are here for
All our Seiko Mods are hand-assembled in our workshop in France, on an authentic Seiko movement, and go through a complete workshop test before shipping (hand alignment, time setting, operation, water resistance depending on the model). Every watch comes with a 2-year warranty, and our after-sales service can be reached directly by email or phone: no chatbot, no third-party platform. In total, that is more than 500 watches assembled and shipped, and 50 customer reviews published on the site with an average rating of 5 out of 5 stars.
Concretely, if you are hesitating between two sizes, write to us with your wrist circumference and the style you are looking for: we will point you in the right direction within 24 hours. It is our job, and it is free.
Our versatile size favourite: SeikoMariner Pepsi 40 mm, the universal sweet spot.
Want to choose everything yourself? Use our Submariner 40 mm configurator or one of our four other configurators.
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