A watch can look wrong on the wrist for three reasons: the case is too big, the lugs overhang the wrist, or the strap is the wrong length. All three can be estimated from one measurement, the circumference of your wrist. This calculator turns it into a proportional range of case sizes, the longest lug-to-lug distance that stays on the flat of the wrist, a matching band width and the strap length range.
How to use the watch band size calculator
- Measure your wrist where you wear a watch. Use a flexible tape or a strip of paper, not too tight and not too loose. Gnomon notes that an open or clenched hand can change the reading by 2 to 3 mm.
- Enter the circumference in centimetres, millimetres or inches.
- Read the results: the width of the flat top of the wrist, the case diameter range, the maximum lug-to-lug distance, the matching band width and the strap length.
- Check the watch. Compare the numbers with the case diameter, lug-to-lug distance and lug width on the watch’s specifications.
Watch band size formula
case diameter = 60% to 75% of the flat top
lug-to-lug ≤ flat top
band width ≈ case diameter ÷ 2
The proportions are from Shinola’s watch size guide and the strap lengths and wrist ranges from the Gnomon Watches band sizing guide (both retrieved 2026-10-16). Gnomon lists strap lengths as tail/buckle in millimetres for wrists of 6 to 7 inches and from 7.5 inches up, so the calculator reports a gap for 7 to 7.5 inches and says when a wrist is outside the published range.
| Wrist circumference | Watch case diameter |
|---|---|
| Under 6 in | Under 36 mm |
| 6 – 7 in (15 – 17.5 cm) | 36 – 42 mm |
| Over 7 in (up to 8 in / 20.3 cm and above) | 42 mm and above |
Calculated sizes for common wrists
| Wrist (in) | Wrist (cm) | Flat top of wrist (mm) | Case 60% (mm) | Case 75% (mm) | Strap length (tail/buckle) |
|---|---|---|---|---|---|
| 5.5 | 14.0 | 46.6 | 27.9 | 34.9 | Shorter than the published range (the shortest listed is 110/70 mm) |
| 6 | 15.2 | 50.8 | 30.5 | 38.1 | 110/70 mm to 125/75 mm |
| 6.5 | 16.5 | 55.0 | 33.0 | 41.3 | 110/70 mm to 125/75 mm |
| 7 | 17.8 | 59.3 | 35.6 | 44.4 | 110/70 mm to 125/75 mm |
| 7.25 | 18.4 | 61.4 | 36.8 | 46.0 | Between 125/75 mm and 130/80 mm (the guide gives no range for 7 to 7.5 in) |
| 7.5 | 19.1 | 63.5 | 38.1 | 47.6 | 130/80 mm to 145/85 mm |
| 8 | 20.3 | 67.7 | 40.6 | 50.8 | 130/80 mm to 145/85 mm |
| 8.5 | 21.6 | 72.0 | 43.2 | 54.0 | 130/80 mm to 145/85 mm |
Worked example
Your wrist measures 17 cm (170 mm), which is 6.69 inches.
- Flat top of the wrist: 170 ÷ 3 = 56.7 mm.
- Case diameter: 60% of 56.7 = 34.0 mm and 75% = 42.5 mm.
- Lug-to-lug: no more than 56.7 mm, so a 52.5 mm lug distance is fine and a 60 mm one would overhang.
- Band width: half the middle of the range (38.25 mm) is about 19 mm, so 18 or 20 mm bands suit.
- Strap length: 6.69 inches is in the 6 to 7 inch band, so 110/70 mm to 125/75 mm.
Choosing a watch and strap
- Lug-to-lug matters more than diameter. A 42 mm watch with a long lug-to-lug distance can look larger than a 44 mm watch with short lugs.
- Band thickness. Larger wrists usually look better with a thicker band; slim wrists with a narrower one.
- Style. Sports watches suit rubber and metal, casual watches suit nylon, and dress watches suit leather.
- If between lengths, choose the longer strap; an extra-short strap binds and an extra-long one hangs.
The proportions are guidelines, not rules, and personal taste matters. For other accessories see the Bangle Size Calculator, Ring Size Calculator and Necklace Length Calculator.
Sources
Every figure above comes from these pages, read directly on the date shown. Brand names are used only to identify published guides.
- Shinola — Watch size guide (60–75% rule, wrist ÷ 3, band width, lug distance) — retrieved 2026-10-16
- Gnomon Watches — Watch band sizes guide (strap lengths X/Y mm, wrist ranges, measuring) — retrieved 2026-10-16
Frequently asked questions
What watch case size suits my wrist?
Shinola says a watch looks proportional when the case is 60 to 75 percent of the width of the flat top of your wrist, and you find that width by converting your wrist circumference to millimetres and dividing by three. For a 17 cm wrist this gives a case of about 34 to 42.5 mm.
What is lug width and how do I measure it?
Lug width is the gap between the two lugs on one side of the case, where the strap fits, and it is always given in millimetres. Common widths run from about 16 to 24 mm, and 20 mm is the most typical. Measure it with a ruler or calipers, or check the strap already on the watch.
How wide should the watch band be?
Shinola says the band is generally about half the diameter of the case, so a 40 mm case suits a 20 mm band. Other common widths are 18, 22 and 24 mm. Larger wrists tend to look better with a wider band.
How long should a watch strap be?
Gnomon Watches writes strap lengths as X/Y mm, tail side over buckle side, without the buckle. For a 6 to 7 inch wrist it recommends 110/70 to 125/75 mm, and for a wrist of 7.5 inches and up 130/80 to 145/85 mm. If a strap is too short choose the longer one.
What is lug-to-lug distance?
It is the distance from the top lugs to the bottom lugs, and two watches with the same case diameter can differ in it. Shinola says to choose a watch whose lug distance fits on the flat of your wrist without overhang. See the Bangle Size Calculator and the Ring Size Calculator for other accessories.