Follow these instructions for accurate Inside and Outside mount measurements.
WIDTH: Measure from left to right in 3 positions (top, middle, bottom). Take the smallest measurement.
HEIGHT: Measure from top to bottom in 3 positions (left, center, right). Take the largest measurement.
Do not make any deductions when you are measuring. The manufacturer will be sure to make them for a perfect fit.
WIDTH: Give the measurements of the space you want to cover from left to right.
HEIGHT: Give the measurements of the space you want to cover from top to bottom.
The width and height measurement should always include the cassette, valence, headrail or roller.
For roller shades, sheer shades, zebra blinds and horizontal blinds the cassette, valence, headrail or roller will be the same width as the measurement given and the fabric will be shortened about 1/2 an inch on each side.
The cassette, valence, headrail or roller will be the same width as the measurement given and the fabric will be shortened about 5/8th of an inch on each side, which is why, for example, if the space to be covered is 60" in width, it is recommended to order 64" (or 2" extra on each side) to ensure that the entire window frame is covered, preventing any light from penetrating through any gaps.