Measuring for horizontal blinds

Inside Mount Installation

For inside mount the factory will make the deduction. Round the measurement down to the nearest 1/8"

To find width:

Measure exact distance to the nearest 1/8" between inside surfaces of window frame at the top, middle and bottom, and use the narrowest width. Do not make any width deductions. Round down to the nearest 1/8"

To find length:

Measure exact distance to the nearest 1/8" from inside surface at top of window to sill at the left, middle and right and use the longest length. If you prefer blind not to touch sill, deduct 1/4". If there is no sill, measure length to point where blind is to reach. Round down to the nearest 1/8"

Outside Mount Installation

For outside mount of blinds, they should extend 2" above moulding to allow for mounting brackets and 2" below moulding if you want to ensure privacy. Round down to the nearest 1/8"

To find width:

Measure exact distance to the nearest 1/8" between the outermost points where the blind is to be placed. For optimum light control, this measurement should extend 2" beyond the window opening on each side (or 4" for the entire width).Round down to the nearest 1/8"

To find length:

Measure exact distance to the nearest 1/8" from where the top of the blind or shade will be located to top of the window sill. If there is no sill or if blind is to overlap window frame measure to point blind is to reach and add 2" to accommodate mounting bracket. Round down to the nearest 1/8"
If you want more privacy add 2" to the bottom if you want your blind to go past the bottom of the window sill.