Composite Door Measuring Guide - Page One     Width: Measure in 3 points; top, middle and bottom and take the smallest measurement and deduct 10mm. Height: Measure again in 3 points; left, centre and right and take the smallest measurement and deduct 10mm. Measure to the underside of the existing cill unless it is NOT going to be replaced. i.e. concrete cill. Diagonals: Ensure the opening is square by measuring the diagonals as shown in red. There should be no more than 5mm difference between each measurement. Repeat the process from the inside of the door from plasterwork to plasterwork make a note of the smallest measurements as before.   This diagram shows how the existing door butts up to the internal plasterline Overall measurements are to the outer edges of the frame. When entering sizes for manufacture they include the cill which is 30mm high if required.    Click for larger diagrams   << Composite Door Measuring Guide - PDF and Do's & Don'ts Composite Door Measuring Guide - Page Two >