The opening of a window or door is almost never perfectly square.
Hinged Panels: Width - Shutters R Us use the formula of minus 3 mm on the Hinge side and minus 3mm on the abutting edge of the panel.
Note we have measured to the smallest square dimension therefore there may appear a gap beyond 3 mm due to the out of squareness.
Height - Our formula deducts 7 mm from the tightest height measurement. Note size dependant, panels will show a slight hinge drop on the open end panel which is industry acceptable if within tolerance.
Face fitted: panels by default are measured to allow for blade clearance then we add 100mm to that width and 100mm to the opening height. (Unless other dimensions are specified).
Sliders: Height - calculated as minus 35mm off the net height for bottom run track system and minus 60 mm if using a top hung system. All panels have a margin of plus 25mm per panel for the overlap of panel width.
Bi fold: Height - shutter panels are calculated as minus 85mm from ceiling to finished floor level (FFL). Note there will appear a light gap between the panel and the top track. There is an allowance of approximately 18mm at the pivot end of an opening and minus 3mm at the free end of the width of the opening to allow for a Bi fold to operate.