Measure around your wrist with a tape measure, just past the wrist bone, where you would actually wear the watch. That single number tells you which case diameters will look proportionate. But diameter alone will mislead you, and the two numbers most people ignore, lug-to-lug span and case height, decide whether a watch is comfortable.
How to measure
Use a soft tailor's tape, or a strip of paper marked with a pen and then held against a ruler. Wrap it snugly but without compressing the skin, sitting just above the wrist bone on the forearm side. Record the circumference in centimetres.
Measure at the end of the day. Wrists swell slightly, and a bracelet sized in the morning can be tight by evening.
A rough starting range
Treat this as a starting point, not a rule:
- Under 15 cm: 32 to 36 mm
- 15 to 16.5 cm: 34 to 39 mm
- 16.5 to 18 cm: 38 to 42 mm
- Over 18 cm: 40 to 45 mm
These ranges overlap deliberately. A 38 mm watch is a small sports watch and a large dress watch at the same time.
The number that actually matters
Lug-to-lug, listed on Claude Bernard product pages as horn gap and, on some sheets, as the total span across the case. A watch overhangs your wrist when the distance between the tips of the lugs exceeds the flat width of your wrist. When that happens the strap cannot sit flat, the watch rocks, and it never feels right no matter how good the diameter looked.
A 40 mm case with short, steeply curved lugs wears smaller and more comfortably than a 38 mm case with long flat ones. If you can only check one number beyond diameter, check this one.
Case height
Height decides whether a watch slides under a shirt cuff and whether it catches on things. Anything under about 9 mm is genuinely thin. Around 10 to 12 mm is normal for an automatic with a date. Divers and chronographs sit higher because there is more inside them.
The Slim Line collection exists precisely for this: slim case profiles for people who want the watch to disappear under a cuff. At the other end, the Aquarider is tall because a 200 m case has to be.
Dial diameter versus case diameter
Two watches with identical case diameters can look completely different depending on how wide the bezel is. A thin bezel gives a large open dial and the watch reads bigger than its measurement. A broad bezel does the opposite.
This is why photographs on a wrist tell you more than a number does, and why it is worth seeing a watch in person at an authorised dealer before committing to a size you are unsure about.
A simple paper test
Print a product image at true size, or draw a circle of the stated diameter on paper, cut it out and lay it on your wrist. It looks crude and it works. It will not tell you about height or lug span, but it settles the diameter question in a minute.
Rectangular cases
Rectangular watches such as Ora Vera are measured differently: width across the case rather than diameter, plus the length down the wrist. A rectangular case almost always wears smaller than a round one of the same nominal measurement, because the corners sit inside where a circle's edge would be.
Common questions
What size watch is best for a small wrist?
Under 15 cm, look at 32 to 36 mm with a short lug span. Case height matters as much as diameter, so favour a thinner case.
Are large watches out of fashion?
Case sizes across the industry have come down from their peak, but fashion is a poor reason to buy. Choose the size that sits flat on your wrist and looks right to you.
Where do I find these measurements?
Every Claude Bernard product page lists Diameter, Case height and Horn-gap in the technical specifications, along with case material, glass, water resistance and strap.
Does strap width matter?
Yes. It is set by the lug width and should be proportionate to the case. Too narrow a strap makes a watch look top-heavy.