Lug-to-Lug
Lug-to-lug is the distance between the tips of a watch's top and bottom lugs. It determines how the watch sits on a given wrist size.
Lug-to-lug (often abbreviated L2L) is the straight-line distance from the tip of the top lugs to the tip of the bottom lugs, measured along the case's vertical axis. It tells you how much wrist real estate the watch will actually occupy.
L2L matters more than diameter for fit on a smaller wrist. A 40mm-diameter watch with a 50mm L2L will overhang a 6.5-inch wrist; a 42mm-diameter watch with a 47mm L2L (e.g. the Tudor Black Bay 58) sits cleanly on the same wrist because the lugs don't push beyond the flat top of the wrist bone. As a general guide: L2L should not exceed about 75-80% of your wrist diameter, or the watch will overhang and shift uncomfortably.
When comparison-shopping, two watches with the same diameter can sit dramatically differently — the difference is L2L and lug shape (downward-curved lugs hug the wrist more than straight lugs of the same length).
Common questions
Is lug-to-lug more important than case diameter for fit?
For fit, usually yes. Two watches with the same diameter can wear completely differently — lug-to-lug and lug curvature decide whether the case overhangs your wrist. Diameter drives dial presence; lug-to-lug drives whether the watch physically sits on your wrist.
What lug-to-lug fits a small (6.5-inch) wrist?
Aim for a lug-to-lug around 47mm or under. A good rule of thumb is that lug-to-lug should not exceed about 75-80% of your wrist's width, or the lugs overhang the flat of the wrist and the watch shifts. A 38-40mm watch with a 46-47mm L2L is a safe small-wrist fit.
How do you measure lug-to-lug?
Measure the straight-line distance from the outer tip of the top lugs to the outer tip of the bottom lugs, along the 12-to-6 (vertical) axis — lugs included, not just the case. Calipers are most accurate; spec sheets list it as 'lug-to-lug' or 'L2L'.