About this tool

Window Blind Size Helper

Turn three width and height measurements into an exact blind order size for inside or outside mount, with depth, squareness and bracket checks.

This helper applies the standard made-to-measure blind rule: for an inside (recess) mount you order the NARROWEST of three width measurements and the LONGEST of three heights, and you subtract nothing, because the factory takes its own deduction — typically 12.7 mm for a venetian, 9.5 mm for a roller and 6.4 mm for a cellular blind. For an outside (face) mount it adds an overlap of 38 mm per side, 75 mm above the opening for the brackets and 50 mm below the sill. It also checks whether the recess is square enough and deep enough to take the blind at all.

How to use Window Blind Size Helper

1. 1

   Open Window Blind Size Helper on AltFTool — it loads instantly in your browser.

2. 2

   Enter the values you already know.

3. 3

   Fine-tune the options to match your scenario.

4. 4

   Read the result and use it in your planning or reporting.

Why use Window Blind Size Helper

• The right one of three

  Narrowest width, longest height — the rule that stops a blind jamming or leaving a gap.

• No double deduction

  Makes clear the factory removes the clearance, so you do not subtract it a second time and end up with a blind that is too small.

• Depth and squareness checked

  Flags before you order when the reveal cannot take a recess fit.

Common use cases

• Converting three tape readings on an out-of-square recess into a single order width you can type into a form
• Checking whether a 60 mm deep reveal is enough for a roller blind to sit fully inside
• Working out the face-fix size when the recess turns out to be 25 mm wider at the sill than at the top

Frequently asked questions