Window Blinds Size Calculator
Blind width and length for inside or outside mount.
Enter your values
Choose one of: Inside mount, Outside mount.
Enter the window/opening width in in.
Enter the window/opening height in in.
Enter the outside mount overlap per side in in.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- Order width
- 35.5 in
- Order height
- 48 in
- Mount type
- Inside mount
Quick answer
Inside mount blinds are ordered slightly smaller than the window opening; outside mount blinds are ordered larger to cover the frame.
inside: order width = opening width - 0.5in; outside: order width = window width + overlap x2
At a glance
| What it does | Blind width and length for inside or outside mount. |
|---|---|
| Category | Home & DIY |
| Inputs needed | Mount type, Window/opening width, Window/opening height, Outside mount overlap per side |
| Main output | Order width |
| Formula | inside: order width = opening width - 0.5in; outside: order width = window width + overlap x2 |
| Cost | Free — no sign-up, no download |
How to use the Window Blinds Size Calculator
- 1Measure the window opening width and height at three points and use the smallest for inside mount.
- 2Choose inside mount for a flush look or outside mount to block more light and make a window look bigger.
- 3For outside mount, add the desired overlap on each side to the actual window width.
Inputs explained
- Mount type
- Choose one of: Inside mount, Outside mount.
- Window/opening width(in)
- Enter the window/opening width in in.
- Window/opening height(in)
- Enter the window/opening height in in.
- Outside mount overlap per side(in)
- Enter the outside mount overlap per side in in.
Worked example
Using the values the calculator loads with:
Inputs
- Mount typeInside mount
- Window/opening width36 in
- Window/opening height48 in
- Outside mount overlap per side3 in
Results
- Order width35.5 in
- Order height48 in
- Mount typeInside mount
Frequently asked questions
How much should blinds be undersized for inside mount?
Typically 1/4 to 1/2 inch total deduction so the blind fits inside the frame without binding.
How much overlap for outside mount?
2-4 inches per side is common to fully block light gaps.
What do I need to enter into the Window Blinds Size Calculator?
Just 4 values: mount type, window/opening width, window/opening height, outside mount overlap per side. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Window Blinds Size Calculator work out the answer?
Inside mount blinds are ordered slightly smaller than the window opening; outside mount blinds are ordered larger to cover the frame. It applies the formula inside: order width = opening width - 0.5in; outside: order width = window width + overlap x2 and shows the working so you can check each step by hand.
Is the Window Blinds Size Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.