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Calculation Machine

Window Blinds Size Calculator

Blind width and length for inside or outside mount.

Reviewed by James Whitfield · How we check our maths

Your values

ⓘ Live results

Results
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.

The formula

inside: order width = opening width - 0.5in; outside: order width = window width + overlap x2

Worked example

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

Result

  • Order width35.5 in
  • Order height48 in
  • Mount typeInside mount

How to use the Window Blinds Size Calculator

  1. 1Measure the window opening width and height at three points and use the smallest for inside mount.
  2. 2Choose inside mount for a flush look or outside mount to block more light and make a window look bigger.
  3. 3For outside mount, add the desired overlap on each side to the actual window width.

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.

About this calculator