Measure your wrist just below the wrist bone, enter the number, and we will give you the case diameter range that suits your wrist, the two-piece strap length to order, and the NATO strap length. Wrist size drives all three, and most people have never measured theirs.
Almost everything about how a watch wears comes down to one number nobody knows about themselves: wrist circumference. It decides whether a case looks proportionate or absurd, whether a stock strap reaches its middle holes, and whether a NATO tail tucks neatly or flaps. Measure once and every strap listing and case spec sheet turns from guesswork into arithmetic.
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How to measure your wrist
The watch sits just below the wrist bone, the knobby bump on the pinky side of your wrist, so measure there, not at the narrowest point further up your arm. Wrap a soft tape flat around the wrist, snug enough that it does not slide but not denting the skin. No soft tape? A strip of paper, a pen mark, and a ruler get you within a millimeter.
The conventions
under 6 in: 34 to 38 mm case · short strap
6 to 6.75 in: 38 to 42 mm case · regular strap
6.75 to 7.5 in: 40 to 44 mm case · regular strap
over 7.5 in: 44 to 46 mm case · long strap
NATO length ≈ wrist + 50 mm of working length
The case ranges are the proportion guidance watch dealers and enthusiast communities converge on. Two-piece straps come in short (about 115/70 mm), regular (about 120/75), and long (about 125/80). A NATO passes under the case and back through keepers, which is where the extra length goes.
Worked example
Your wrist measures 6.9 inches (17.5 cm). That lands in the 6.75 to 7.5 band, so cases from 40 to 44 mm suit it, and a regular 120/75 strap reaches its middle holes. For a NATO: 6.9 inches is 175 mm, plus 50 mm of working length is 225 mm, comfortably inside the standard 270 mm NATO with tail to tuck. A 36 mm dress watch would wear small but wearable; a 47 mm diver would wear like a dinner plate.
The proportion rule nobody states
Case guidance is really about lug-to-lug distance, the tip to tip span of the watch across your wrist, which runs 8 to 12 mm longer than the dial diameter. The watch stops looking right when the lugs overhang the flat of your wrist. A flat, wide 6.5 inch wrist can carry a 44 mm sports watch that a round 7 inch wrist cannot. So treat the ranges above as your shortlist, then check one spec before buying: if the lug-to-lug measurement exceeds your wrist's flat width, size down no matter what the chart said. And whatever you buy, match the strap to the lug width exactly; it is the one number with no tolerance in it.
Frequently asked questions
How do I measure my wrist for a watch?
Wrap a soft measuring tape around your wrist just below the wrist bone (the knobby bump on the pinky side), which is where a watch actually sits. Keep the tape flat and snug without compressing the skin. Most adult wrists measure between 5.5 and 8 inches, or 14 to 20 centimeters.
What watch case size fits my wrist?
The widely used guidance: wrists under 6 inches wear 34 to 38 mm cases well, 6 to 6.75 inch wrists suit 38 to 42 mm, 6.75 to 7.5 inch wrists suit 40 to 44 mm, and larger wrists carry 44 mm and up. These are conventions about proportion, not laws, but stray far outside them and the watch reads as either a coin or a wall clock on your arm.
What do two-piece strap lengths like 120/75 mean?
A two-piece strap comes as a long half (the one with the holes) and a short half (the one with the buckle), measured in millimeters. A 120/75 strap has a 120 mm holes side and a 75 mm buckle side. Regular straps around 120/75 fit wrists of roughly 6.5 to 7.5 inches; short straps near 115/70 suit smaller wrists and long straps near 125/80 suit larger ones.
How long should a NATO strap be?
A NATO wraps under the watch and doubles back through a keeper, so it needs your wrist circumference plus roughly 2 inches (50 mm) of working length; the standard 270 to 280 mm NATO fits most wrists with tail to spare and extra tail tucks back into the keepers. If you are near the small end of wrists, look for short NATOs around 240 mm so the tail does not lap the watch.
Does lug width matter when buying a strap?
It is the one measurement that is not negotiable. Lug width is the gap between the watch's lugs where the strap mounts, usually 18, 20, or 22 mm, and the strap must match it exactly. Check the watch's specs or measure the gap with a ruler before ordering any strap; a 20 mm strap in a 22 mm gap rattles, and a 22 in a 20 does not fit at all.
Do watch bracelets need sizing too?
Metal bracelets size by removing links rather than choosing a length, and most come long enough to fit an 8 inch wrist out of the box. The useful number is still your wrist measurement: a jeweler (or a link tool and ten minutes) takes the bracelet to your wrist plus about a quarter inch of comfort room, enough to slide one finger under.