Calculate blind or window width and height from the other dimensions using a 2-inch outside-mount allowance and converting between in, ft, cm, and m.

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

This blind size calculator uses a simple outside-mount sizing rule: add 2 inches total to the window width and 2 inches total to the window height. That is usually interpreted as about 1 inch of overlap on each side and about 1 inch of extra coverage at the top and bottom.

BW = WW + 2
BH = WH + 2

When you enter the blind size instead of the window size, the calculator reverses the formula:

WW = BW - 2
WH = BH - 2
  • WW = window width, in inches
  • WH = window height, in inches
  • BW = blind width, in inches
  • BH = blind height, in inches
  • 2 = total outside-mount allowance, in inches

The calculator can fill in missing window or blind measurements as long as you enter at least one width value and one height value. If you enter a window width, it calculates blind width by adding 2 inches. If you enter a blind width, it calculates window width by subtracting 2 inches. The same rule is used for height.

The calculator also supports inches, feet, centimeters, and meters. Internally, it converts measurements to inches, applies the 2-inch allowance, then converts the result back to the unit selected for the output field.

Typical Blind Measuring Allowances

The calculator uses a 2-inch total allowance for an outside mount. Actual recommendations can vary by blind type, window trim, and manufacturer instructions.

Mount type Typical width approach Typical height approach Notes
Outside mount Window width + 2 in total Window height + 2 in total Matches this calculator’s rule.
Inside mount Use exact inside opening width Use exact inside opening height Do not add the 2-inch outside allowance.
Greater light blocking Window width + 3 to 4 in total Window height + 3 to 4 in total Useful when you want more overlap around the frame.

Unit Conversions Used for Blind Measurements

Unit Conversion to inches Example
Inches 1 in = 1 in 36 in = 36 in
Feet 1 ft = 12 in 3 ft = 36 in
Centimeters 1 cm = 0.3937 in 100 cm = 39.37 in
Meters 1 m = 39.3701 in 1.5 m = 59.06 in

Example Blind Size Calculations

Example 1: Calculate blind size from window size

You measure a window that is 34 inches wide and 58 inches high.

  • Blind width = 34 + 2 = 36 inches
  • Blind height = 58 + 2 = 60 inches

The estimated outside-mount blind size is 36 in by 60 in.

Example 2: Calculate window size from blind size

You have a blind that is 42 inches wide and 66 inches high, and you want to check the matching window size using the calculator’s rule.

  • Window width = 42 – 2 = 40 inches
  • Window height = 66 – 2 = 64 inches

Using the 2-inch outside-mount allowance, the matching window size is 40 in by 64 in.

FAQs

Does this calculator work for inside-mount blinds?

Not directly. This calculator uses an outside-mount rule that adds 2 inches total to the window width and height. For inside-mount blinds, you usually measure the inside of the window opening and do not add outside overlap. Many manufacturers make their own small deductions for inside mounts, so check the product instructions before ordering.

Is the 2-inch allowance added to each side or total?

The calculator adds 2 inches total. For width, that means about 1 inch on the left and 1 inch on the right. For height, that means about 1 inch at the top and 1 inch at the bottom.

Why does the calculator reject some window and blind measurements entered together?

If you enter both a window measurement and a blind measurement for the same direction, they must match the calculator’s rule. For example, a 35-inch window width should pair with a 37-inch blind width. If the values do not match within a small tolerance, the calculator asks you to correct or clear one of the fields.