Looking for the perfect fit for a new window treatment? It all starts with an accurate measurement. First, determine if the window treatment will be installed as an inside mount or an outside mount. Use a metal tape measure to measure accurately to the nearest 1/8th inch. Do not take deductions. Inside mount treatments are installed inside the window casing. Measure the inside of the window frame in three places for width: across the top, middle and bottom. And for height: at the left, middle and right side. Record the narrowest width and longest height. Don’t forget to record window depth so you’ll meet the minimum installation requirement. Outside mount window treatments are mounted outside the window casing. Measure the overall area to be covered. Consider adding an extra 3 inches to the width and height for optimum light control and privacy. Outside mounts require at least 2 inches of flat surface above the window or frame for mounting brackets. Projection brackets may be needed to clear the frame moulding. Most hardware packages come with everything you need for installation in wood or drywall. For metal or masonry, make sure you have the right drill bits and appropriate screws needed for installing window treatments.