Just like the width, to measure for a recess drop we would always ask you to measure in three places across the internal window opening, and to provide us with the smallest measurement.  With all blinds, apart from roller blinds, a small deduction will be taken to ensure the blind can operate without hitting the window sill.  This is especially important for venetian and wooden blinds to ensure there is enough room for the slats to tilt.

If your blind does not sit within a recess or you are replacing a blind in situ you may want to ensure we do not deduct anything from the drop.  If this is the case, please provide the exact size from the top of the blind to the very bottom.  

For vertical blind slats only however, please ensure that you only measure the fabric 'drops' excluding the headrail, from the top of the fabric to the bottom.  For a vertical blind you can measure from the top of the headrail to the bottom of the fabric slats.  Unsure - Please feel free to call our expert customer services team or refer to the detailed measuring guides.