Fitting a Venetian Blind Inside the Window Recess (Recess)Please note that it is advisable to measure the width in several places, as stated above, and you should of course quote the lowest measurement for both width and drop.
Fitting a Venetian Blind Outside the Window Recess (Exact)
Width - Decide how much you wish the blind to overlap the recess at each side. To minimize light leakage it is recommended that the blind overlaps the window recess by least 6.5 cm (2.5") each side.
Drop - When measuring the drop, take into account the required space for the mounting bracket; a flat surface of a minimum 50mm is required.
When raised, the blind ideally should not obscure the window. Therefore blinds must be fixed high enough above top of window recess to allow for depth of headrail and bunched slats. To allow for this add 44mm (1.75") plus 12mm (0.5") for every foot of blind depth.
The overlap at the bottom of the blind is a matter of personal choice, but please take into account common obstacles such as radiators when measuring.