Blind Size Calculator
Calculate the correct window blind size for inside mount or outside mount installation.
Formula
Inside: W = window width − 1/4 in; Outside: W = window width + 2×overlap
- Inside mount: deduct 1/4 inch from width for easy installation.
- Outside mount: add 2–3 inches on each side and above the window.
- Always measure at least 3 points (top, middle, bottom) and use the smallest width for inside mount.
36×48 in window, inside mount
Inputs
- Window Width: 36 in
- Window Height: 48 in
- Mount Type: inside
- Outside Overlap (each side): 2 in
Inside mount blind: 36 − 0.25 = 35.75 in wide × 48 in tall.
Frequently asked questions
What is inside vs outside mount?
Inside mount fits within the window frame; outside mount attaches to the wall above and outside the frame.
Why deduct 1/4 inch for inside mount?
This small deduction ensures the blind can raise and lower without rubbing the frame.
How much overlap is recommended?
2–3 inches on each side and 2 inches above for outside mount provides good light blockage.
What if my window is not square?
Measure in at least 3 places and use the smallest measurement for inside mount.