Overview
Measure the area the outside frame will cover. Architraves, square-set openings and projecting sills use different boundaries and allowances. Follow the matching method rather than adding a standard amount to every opening.
Measuring for an Outside Mount
Choose the outside measuring method that matches the window. Architraves normally define the coverage boundary; square-set openings need the stated frame allowances. A projecting sill changes the bottom reference. Do not transfer figures from a recess-fit measurement without checking these differences.
Measuring Outside Mount for a Square-Set Window
For My Direct's square-set face-fit method, measure the opening in three places in each direction and use the smallest width and drop. Add 42 mm at each side: 84 mm to the width and 84 mm to the drop.
If a sill projects at the bottom, add only at the left, right and top: 84 mm to the width and 42 mm to the drop. The bottom finishes on the sill. These are frame coverage allowances, not factory deductions.
Measuring Outside Mount with an Architrave
Take three widths between the outer left and right architrave edges. Take three drops between the outer top and bottom edges. Use the largest width and largest drop so the frame covers the trim at every point.
Measuring Outside Mount for a Window with a Sill
For a square-set opening with a projecting sill, measure three widths inside the opening and three drops from the sill top to the opening top. Use the smallest readings under My Direct's square-set method. Add 84 mm to the width and 42 mm to the drop for the left, right and top frame coverage only.
Measuring Outside Mount for a Window with a Sill and Architrave
Measure three widths between the outside architrave edges. Measure three drops from the sill top to the upper outside architrave edge. Use the largest width and largest drop. Do not add the square-set allowances to dimensions already taken over the architrave.
