How do you get accurate windows measurements before ordering blinds or shades?

For inside mount: Measure the width of the window opening at the top, middle and bottom of the window. Use the smallest of these 3 measurements to order you blinds or shades. Measure the height on the far left, middle, and far right of the window and use largest height measurement when placing your order. For outside mount: Measure the full width of the area you want to cover with the blind or shade shade and, if space permits, add an extra 3 1/2 to each side to eliminate light leakage. Measure the full height of the area you wish to cover with the shade and add 1 1/2" to 2" to encompass the flat mounting surface area. Add additional inches to account for things like molding or framework that you wish to cover with the window covering. The minimum flat space needed for the bracket is listed in the specification section for each product.