This guide applies to all blind types.
Measure the width and height that you would like your blind. This measurement is called "Outside Recess".
Your blind will be made exactly to your given sizes, including brackets.
Measure the width and height of your window recess from wall to wall. Take measurements at three different points just in case your window is not square and write down the smallest measurement. This measurement is called "Inside Recess".
A small deduction will be made from your measurements to ensure your blind can operate smoothly and fits within the recess.