How to Fit Blinds | Measure, Mount & Finish Right

Fitting blinds starts with accurate measurements and choosing inside or outside mount, then installing brackets level and secure before snapping the blind into place.

One wrong measurement and the blind arrives too wide for the window — or leaves ugly light gaps. Fitting blinds requires three distinct phases: precise measuring, solid bracket installation, and a final test to catch binding or obstructions before the blind is fully mounted. Here is the exact sequence that works for roller blinds, vertical blinds, and shades, with the rules that apply to every window.

Measure the Window First — Inside or Outside Mount

The type of mount determines how you measure. An inside (recess) fit places the blind inside the window frame for a built-in look; an outside (face) fit mounts on the wall or frame above the opening for maximum light blockage. Measure width at three points — top, middle, bottom — and use the narrower measurement for inside mount, and the widest measurement for outside mount. The Shade Store notes that inside-mount width should be the shortest of the three width points, while the drop uses the longest.

For an inside fit, also measure depth at the shallowest point — a recess that is too shallow won’t hold the headrail or slats. Home Depot’s guide warns that if the blind is wider than the opening, it simply will not fit. For outside mount, add at least 3 inches on each side for good coverage, and roughly 4 inches above the frame to block light from the top.

Install the Brackets Level and Secure

Mark the bracket positions with a pencil, using a level to keep them aligned — an unlevel bracket will cause binding and uneven gaps. The exact distance from the top corners varies by manufacturer, so check the blind’s instruction sheet before drilling. Drill pilot holes first, then insert the appropriate wall fixings for your wall type. Dunelm specifically warns to choose suitable rawlplugs for plasterboard, brick, or timber. For vertical blinds, BlindsDirect says mounting clips should never be more than 60 cm apart.

Once the brackets are secure, slide or snap the headrail into them. Some systems use a swivel lock, others need small bracket covers to hold the rail. Take your time here — a crooked bracket is the single most common cause of blinds that don’t operate smoothly.

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Test Before Tightening Everything

Before finalizing the screws, test the blind by raising and lowering it, and rotating slats. Check that no part of the blind hits the window handle, latch, or any obstruction. If the blind binds or won’t roll fully, the brackets may need a slight shift. For corded blinds, attach the safety device — a cord tensioning clip — now rather than after the blind is fully seated. Speedy Services notes that these clips are especially important in homes with children or pets.

If the blind slides forward or sits unevenly in the brackets, remove it and check that the headrail is seated fully. Some systems need the bracket tabs pushed down or a locking cover snapped on. When everything operates smoothly and the blind sits flush, tighten the final screws and install any trim or valance that came with the unit.

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