Work out door size instantly with clear inputs, formula shown and shareable results.
Door leaf size is the structural opening minus the frame on each side and a fitting clearance. The figure that matters for access is the clear opening with the door open at 90 degrees, which is smaller again by the door thickness and hinge projection.
Door sizing
leaf width = opening - 2 x frame - 2 x clearance; clear opening = leaf width - door thickness allowance
800 mm is the usual new-build requirement, with 750 mm accepted in existing buildings. A 900 mm structural opening only just achieves it.
To allow for floor covering thickness and to leave a threshold gap so the door does not bind on carpet.