Door sizing is one equation wearing two costumes. Learn the frameless version, adjust for frames, and schedules write themselves.
Frameless formula
Door = opening + (2 × overlay) − reveal allowance. Standard euro: 16 mm overlay each side with 3 mm gaps between fronts — an 800 mm double-door opening yields two doors of 397 mm. Consistency of reveal matters more than the number chosen.
Face-frame translation
Overlay measures onto the frame, not the opening: half-inch and five-eighths partial overlays dominate US stock; full-overlay frames take 1¼-inch-plus with the right hinge arm. Confirm hinge spec before sizing, not after.
The sanity pass
Adjacent doors share gap lines — check totals across a run against carcass total before ordering. Tall pantry pairs and corner-cabinet doors are where a five-minute check saves a two-week remake.