Round holds 80% of the market as the most common form in watchmaking. The reason is two-sided. Mechanically, the mainspring, balance wheel, and escapement gear-train rotational architecture fits naturally inside; CNC machining is easier and gasket sealing lines are simpler. Ergonomically, the curves match the natural arc of the wrist; at the same diameter the round case sits the most comfortable.
The industry's icons live in the round form. The Rolex Submariner at 40-41mm, GMT-Master II, Datejust, Daytona — all round. The Omega Speedmaster Moonwatch at 42mm and the Seamaster Diver 300m are round; the Patek Philippe Calatrava 5226G is the round dress-watch classic; the A. Lange & Söhne Saxonia, the JLC Polaris, the IWC Pilot 41 all belong to the round family. On the sport side the Tudor Black Bay 58 at 39mm, the Tag Heuer Carrera at 39mm, the NOMOS Tangente Datum at 35mm — round in form, different in dimension.
The practical call rotates around the lug-to-lug measurement. A 40mm case with a 48mm lug-to-lug sits clean on a 17cm wrist; 52mm+ overhangs. The Submariner at 40mm/47.5mm lug-to-lug is the middle of the road. The Speedmaster at 42mm/47.5mm lug-to-lug reads smaller than its 42 because of the lug spec. On a round case thickness also matters: dress at 8-10mm (Calatrava), sport at 11-13mm (BB58), tool or diver above 14mm (Pelagos LHD). The round dominance carries on today, but the Cartier Tank (rectangular), the AP Royal Oak (octagonal), and the TAG Heuer Monaco (square) stay strong as out-of-category statement pieces.
