· by Michael Blair, Nashville's Shutters and Blinds
Custom blinds are manufactured to the measurements you supply, so a wrong number usually cannot be sent back; check the seller’s return policy before you order. The rules differ between inside and outside mount, so settle which mount the window needs first and then measure for that one. Bali, Norman and Hunter Douglas each publish their own measuring advice, and where they disagree, the instructions for the blind you are actually buying win.
How do you measure for an inside mount?
For an inside mount, Bali’s measuring guide for wood and faux wood blinds says to measure the inside width of the casing in three places and record the narrowest, then measure the height in three places and record the longest. Height is where the brands part ways. Norman’s guide to measuring for window treatments takes the longest of three heights for horizontal blinds but the shortest for vertical blinds and for inside-mounted shutters, so read the sheet for the product on your order.
The same Bali guide says to take no deductions for clearance, because the factory takes them. That factory deduction is why an inside-mount blind lets a thin line of light through down each side, and a second deduction taken at home only widens it. Measure corner to corner both ways while the tape is out: Hunter Douglas’s installation advice uses the diagonals to show whether a window is square and suggests an outside mount for one that is not, a case we walk through in our post on shutters for out-of-square openings.
How do you measure for an outside mount?
Measure the area you want covered, then add overlap on each side and above so light does not leak around the edges. How much depends on whose blind it is. Bali recommends 1½ inches on each side, 3 inches across the width, while Norman tells you to add 4 inches to both the width and the height.
Look at the wall above the window before you write the number down. Bali’s guide says outside mount brackets need at least 2 inches of flat surface above the window or on the window frame, and that projection brackets or shims can be ordered to clear a frame or molding that gets in the way.
- Inside mount: narrowest of three widths, height as the brand’s sheet says, no deductions unless the sheet asks for them
- Outside mount: add the overlap the brand recommends on each side and above
- Steel tape, never cloth
- Measure every window individually, even identical-looking ones
- Check depth for inside mount clearance
Depth matters
Inside mount needs enough depth in the casing for the headrail, and the figure changes with the product and even the lift. Bali gives ¾ inch as the minimum depth for an inside-mount wood blind, and its measuring guide for cellular and pleated shades lists one depth for a headrail that sits partly recessed and a larger one for a headrail fully recessed flush with the casing.
A shallow casing may allow only a partial recess or push the window to an outside mount. Shutters have a test of their own: Norman says the opening needs enough depth for the louvers to rotate, and recommends an outside mount when it does not have it. That depth is one of the first things we check on a plantation shutter visit.
Measure every window
Windows that look identical often are not, and the Bali guide warns that size variances are common. Bali’s measuring page lists a steel tape measure, never a cloth one, and asks for each window to be measured individually and rounded to the nearest ⅛ inch. Label every measurement by room and position.
That labeling matters at installation, when a stack of near-identical blinds arrives and each one needs matching to its opening. On our blinds and shutters the person who installs is the person who measures, and every opening is measured on site, which is also what Hunter Douglas recommends. If you would rather not order from your own numbers, ask us for a free estimate and we will measure it for you.
Sources
- Bali Blinds (Springs Window Fashions), Measuring Guide for Wood Blinds and Faux Wood Blinds — Inside mount: narrowest of three widths, longest of three heights, no deductions (the manufacturer takes them); factory deduction lets light spill at the sides; 1½ inch overlap per side for outside mount; 2 inches of flat surface for brackets; ¾ inch minimum inside-mount depth; steel tape, size variances common
- Norman, How to Measure for Blinds & Window Treatments — Longest height for horizontal blinds, shortest for vertical blinds and inside-mount shutters; add 4 inches to width and length for outside-mount blinds; shutters need depth for louvers to rotate; round to the nearest ⅛ inch
- Hunter Douglas, Window Treatment Installation & Operation — Measure top, center and bottom and both sides and center, then diagonally to check square; outside mount for a window that is not square; recommends a professional to measure and install
- Bali Blinds (Springs Window Fashions), Measuring Guide for Cellular and Pleated Shades — Separate minimum depths for a partly recessed and a fully recessed headrail, by cell size and lift; no deductions for clearance on inside mount
- Bali Blinds, How to Measure Windows for Blinds and Shades — Steel tape measure, never cloth; measure each window individually; round to the nearest ⅛ inch
FAQ
Measuring for Blinds Without Getting It Wrong — questions
Should I deduct anything for inside mount blinds?
Usually not. Bali’s measuring guides for wood blinds and for cellular shades both say to give the exact narrowest width and let the factory take the clearance deduction. That deduction already leaves a thin line of light down each side, so taking a second one at home makes the gap wider, and a blind made to order cannot be stretched to close it. Check the instructions for the brand you order, since that is the sheet the factory works from.
How much overlap for an outside mount?
It depends on the maker. Bali recommends 1½ inches on each side, 3 inches across the width, and Norman’s guide says to add 4 inches to the width and the height. More overlap means less light around the edges. Also check the wall above the window, because Bali says its outside mount brackets need at least 2 inches of flat surface there.
Do I need to measure every window separately?
Yes. Openings that look the same often are not, and Bali’s measuring guide says size variances are common. Measure each one, round to the nearest eighth of an inch, label it by room and position, and keep the list, because it matters again at installation when several similar blinds need matching to the right openings.
How do you measure for wood blinds?
Bali’s guide for wood and faux wood blinds says to measure the inside width of the casing in three places and keep the narrowest, then the height in three places and keep the longest, with no deductions. Check for at least ¾ inch of depth. For an outside mount, add 1½ inches on each side.