Updated July 2026

How to Measure Windows for Custom Blinds

Accurate measurements are the difference between a blind that looks custom and one that looks cut-rate. Follow these six steps if you're measuring yourself — or skip the tape entirely and let us do it in person, free.

1. 1

   Decide inside or outside mount

   Inside mount sits flush inside the window frame for a clean look — you need at least 2 inches of frame depth. Outside mount sits on the wall above the window and is best when the frame is shallow or the window is not square.

2. 2

   Measure the width in three places

   Using a steel tape measure, measure the width at the top, middle, and bottom of the window opening. Record all three. For inside mount, use the smallest number. For outside mount, add 3–4 inches on each side for light blockage.

3. 3

   Measure the height in three places

   Measure the height on the left, centre, and right of the opening. For inside mount, use the largest number so the blind fully covers. For outside mount, measure from where the blind will start to where it will end.

4. 4

   Check that the window is square

   Measure the two diagonals corner to corner. If they differ by more than 1/4 inch, the window is out of square — tell your installer, as it affects mount type and reveal.

5. 5

   Note the frame depth

   Measure from the front edge of the frame to the glass. This determines whether an inside-mount cassette or valance will fit flush.

6. 6

   Write it all down

   Record every measurement to the nearest 1/8 inch, in inches. Label each window (e.g. 'Master bedroom north window') and note left/right if the room has multiples.