If you have opted to have your blind fitted inside the recess,
you need to record the exact width and drop. As variations
may occur within the window recess, you should take the width
and drop measurements in three places - the sides and in the
middle - and record the shortest of the three widths and the
longest of the three drops.

This means that your blind will not snag on the sides of the recess and will be a perfect length to the sill. Please always give measurements in millimeters.

Be aware of any handles or other window furniture which would
affect the smooth operation of your blind.

Measuring for a blind to be fitted outside the recess could not
be simpler. Decide how much overlap you want at the sides, top
and bottom and add these to your measurements. Please record sizes in millimeters.