Measured: Case size is quoted in millimeters across the case, excluding the crown. Round cases quote a diameter, and the rest quote width by height. Lug to lug length decides whether it fits your wrist.
The basics
What to know about case shape
Case shape is the outline a watch draws on your wrist, and it settles more than style. The shape decides how the case seals against water and how easily a crystal can be replaced. It also decides how much wrist the watch actually covers, which is not what the headline number tells you.
Sizes are quoted in millimeters across the case, excluding the crown: a diameter for round cases, width by height for the rest. The figure that decides fit is lug to lug, the distance from the tip of one lug to the tip of the opposite one. Once lug to lug passes the flat top of your wrist, the lugs overhang and the watch wears oversized whatever its diameter says.
Judge the shapes on sealing and servicing as well as looks. Circles take gaskets easily and dominate anything water resistant, while corners and curves need shaped crystals and custom seals that cost more to replace. Thickness completes the picture, since a slim case slides under a cuff and a thick one fights it.
