Using a metal tape measure take the width of the visible window frame at the top, middle and the bottom of the frame. Record the narrowest measurement.

If there are any obstructions within the recess such as a dado rail or part tiling measure between the obstructions. Next measure the height of the visible frame at both sides and the middle. Record the smallest measurement.

To measure for a blind intended to fit outside the window recess we recommend an overlap of 100mm to each edge as shown in the illustration.Measure as for a recess fit  (above) and add 200mm to each measurement. If the cill protrudes far enough to obstruct the blind only add 100mm to the drop and allow the blind to sit on the cill.