Case diameter is only one part of fit. Lug-to-lug length, thickness, dial opening, bracelet taper and wrist shape all affect how large a watch feels.
Case diameter
Diameter gives a quick comparison, but two watches with the same diameter can wear differently because of bezel width and dial size.
Lug-to-lug length
This measurement often predicts overhang better than diameter. Ideally, the lugs should sit comfortably within the top surface of the wrist for a conventional fit.
Thickness
Thicker watches feel more substantial and may catch on shirt cuffs. Mechanical complications and robust water-resistant cases often increase thickness.
Bracelet sizing
Check whether the bracelet uses removable links, half-links or micro-adjustment. A luxurious-looking gold bracelet is disappointing if it cannot be sized accurately.
Measure an existing watch
The most reliable starting point is a watch you already enjoy wearing. Compare its diameter, lug-to-lug and thickness with the model you are considering.