In short. For a wrist under 16 cm (6.3 in), go for 36 mm; between 16 and 18 cm, 39 or 40 mm; above 18 cm (7.1 in), 41 mm. Lug-to-lug width and thickness matter as much as diameter: this guide helps you decide before you order.
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 watch 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 1,000 watches to date, and our customers have left us 69 reviews published on the site with an average rating of 4.9/5. 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 watch 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 watch mods suited to every profile.
2. Correspondence table: wrist circumference and watch mod diameter
Here is the table we use in the workshop to guide new customers.
| Wrist circumference | Ideal case diameter | Recommended watch models |
|---|---|---|
| Under 15 cm | 36 mm | — |
| 15 to 16 cm | 36 to 39 mm | — |
| 16 to 18 cm | 39 to 40 mm | — |
| 18 to 19 cm | 40 to 41 mm | — |
| Over 19 cm | 41 mm and up | GMT Blue or White, SUB MOD on a wide 3-link 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 SUB MOD watch 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 watch 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:
- 22 mm for the 41 mm GMT: a confident sporty presence
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.
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 SUB MOD 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.
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.
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. You cannot go wrong.
5. FAQ: the 5 questions we get asked most in the workshop
Is a 40 mm watch 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. 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 watch mod be shortened?
Yes, and it is included with shipping. 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 SUB MOD 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 watch mods are hand-assembled in our workshop in France, on a genuine Japanese 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 1,000 watches assembled and shipped, and 69 customer reviews published on the site with an average rating of 4.9/5.
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: SUB MOD Pepsi 40 mm, the universal sweet spot.
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