Why it matters more than case diameter
Your wrist has a flat top and then curves away. A watch looks right when its lugs end on that flat surface, and too big when they reach past it and hang over the edge. Case diameter measures the case side to side, which never touches that edge; lug-to-lug measures the direction that does.
Two watches with the same diameter can wear very differently. Among the 44 40 mm watches in the almanac, the Doxa SUB 250T GMT Professional 855.10.351.10 measures 42.9 mm lug-to-lug, while the Tissot PRX Powermatic 80 40mm T137.407.11.041.00 measures 51 mm. That 8.1 mm gap is the difference between a watch that sits inside a 6.5-inch wrist and one that overhangs it.
This isn't a one-off: across every round watch we've measured, case diameter is a poor guide to how long a watch is.
How to measure lug-to-lug
- Lay the watch face up with the strap or bracelet open.
- Measure in a straight line from the tip of the lugs at 12 o'clock to the tip of the lugs at 6 o'clock, through the center of the dial.
- Use calipers if you have them; a ruler read from directly above works to within a millimeter.
Watch for bracelets with a rigid first link. On integrated designs like the Tissot PRX, the first link can't bend, so the watch wears as if its lug-to-lug were several millimeters longer. We record the as-worn figure for those.
Lug-to-lug vs lug width
They sound alike but answer different questions. Lug-to-lug is the watch's length and tells you whether it fits your wrist. Lug width is the gap between the two lugs on one side, usually 18, 20 or 22 mm, and tells you which straps fit the watch. See watches by lug width.
What lug-to-lug should you look for?
Measure the flat top of your wrist and subtract about 4 mm. Our watch size chart lists the number for every wrist size, and the fit finder checks it against every watch we've measured.