Lug-to-lug distance

Lug-to-lug distance — also called lug span — is the measurement in millimetres that separates the tip of the upper lug from the tip of the lower lug, measured with the case laid flat along the vertical axis. It is one of three fundamental dimensions of a case, alongside diameter and thickness, and it is often the one that truly determines whether a watch wears well or poorly.

The point I see ignored continuously, even in serious publications, is this: diameter and lug-to-lug distance do not move in parallel. A 38 mm case can have a lug-to-lug value of 46 mm, like the Villeret Ultraplate, and wear decently on almost any wrist. A 42 mm case with extended lugs can exceed 51 mm and spill over onto the carpal area or tendon. I have seen 18 cm wrists wear certain 44 mm watches without issue and categorically reject certain 40 mm watches for precisely this reason. The number on the dial does not tell the whole story.

The correct measurement is taken with a calliper, placing the watch on a flat surface: from the tip of the upper lug to the tip of the lower lug, in a straight line. Some sources indicate the midpoint of the spring bar holes; in practice the two readings differ little, but for rigorous technical sheets the second convention applies. The problem is that manufacturers are not uniform: I have compared factory specifications with bench measurements and discrepancies often reach one millimetre, rarely two.

Visually, a lug-to-lug distance that is modest relative to the case diameter gives compact proportions and a collected appearance. When the lugs extend instead — for technical reasons related to the height of the caseback or for aesthetic choice — the watch acquires a different presence, more horizontal on the wrist, which some prefer and others do not.

From my experience at the bench: whoever has a wrist that is short anteroposteriorly suffers more from an elevated lug-to-lug than from a generous diameter. It is the first measurement I look at when someone brings me a watch complaining that it "does not wear well". Often the problem is not where they think.