Free · Everyday planning calculators

Blind Opening Measurement Planner

Compare the smallest of three width and height measurements for inside and outside mounting.

  • Formula & worked example
  • Private in your browser
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

Widths 100, 99 and 101 cm give 99 cm; the 149 cm minimum height becomes 148.365 cm under the quarter-inch deduction.

Opening = minimum of three measures; outside additions = 3 in wide and 1.5 in tall

Worked example

Enter these known values and leave the other values blank.

Hanging style
Inside mount
Width top
100 cm
Width middle
99 cm
Width bottom
101 cm
Height left
150 cm
Height center
149 cm
Height right
151 cm
Width
99 cm
Length
149 cm
Length (not resting on sill)
148.37 cm

Assumptions and limitations

  • The source uses the smallest width and height. Its inside height deducts a quarter inch; outside sizing adds three inches in width and one and a half inches in height. Manufacturer instructions may use different deductions.

Common questions

What does this estimate assume?

The source uses the smallest width and height. Its inside height deducts a quarter inch; outside sizing adds three inches in width and one and a half inches in height. Manufacturer instructions may use different deductions.

Can I find a missing input?

Clear the unknown field and enter compatible known values. The controls retain supported inverse calculations, while rounded counts and one-way outputs stay directional.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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