Enter the width and height of your window to estimate an outside-mount blind size. This calculator uses a simple rule-of-thumb that adds 2 inches total to each dimension (about 1 inch per side/top/bottom). For inside-mount blinds, you typically do not add inches—follow the manufacturer’s measuring and deduction instructions.

Blind Size Calculator

Enter at least 2 values: one width (Window Width or Blind Width) and one height (Window Height or Blind Height). The calculator fills the remaining fields using a +2 in (total) outside-mount allowance.

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Blind Size Formula

The following rule-of-thumb is used in this calculator to estimate an outside-mount blind size. (Inside-mount sizing is different—follow your manufacturer’s instructions.)

BW = WW + 2
BH = WH + 2

Variables:

  • BW is the blind width (inches)
  • WW is the window width (inches)
  • BH is the blind height (inches)
  • WH is the window height (inches)

For this basic outside-mount estimate, add 2 inches to both the width and height of the window dimensions (2 inches total per dimension, not per side). In real installations, the needed overlap can vary by mount type, blind type, and desired light/privacy control—always confirm measuring requirements before ordering.

What is Blind Size?

Blind size refers to the dimensions of window coverings (blinds or shades) ordered to fit a window. Depending on whether you choose an inside mount or outside mount, the ordered size may closely match the window opening or may include added overlap to cover the frame/trim. Proper sizing helps achieve the desired privacy, light control, and appearance.

How to Calculate Blind Size?

The following steps outline how to calculate the Blind Size.

  1. Measure the width of the window (WW) in inches.
  2. Measure the height of the window (WH) in inches.
  3. For the basic outside-mount estimate used here, add 2 inches to the window width to get the blind width (BW).
  4. For the basic outside-mount estimate used here, add 2 inches to the window height to get the blind height (BH).
  5. Use the calculator above to verify your measurements. (For inside mounts, do not use the +2 rule—follow the manufacturer’s sizing/deduction guidance.)

Example Problem : 

Use the following variables as an example problem to test your knowledge.

window width (WW) = 30 inches → blind width (BW) = 32 inches (using BW = WW + 2)

window height (WH) = 48 inches → blind height (BH) = 50 inches (using BH = WH + 2)