How to Measure Your Windows for Custom Blinds

An inside mount sits inside the window opening for a clean, built-in look. It requires enough depth for the headrail and a square, undamaged frame. An outside mount attaches to the wall or trim above the window, hides an out-of-square opening, and blocks more light around the edges.

In Tampa homes we choose outside mount most often for bedrooms — the extra coverage is what makes a blackout shade genuinely dark — and inside mount for living areas where the trim is worth showing.

Use a steel tape, never a cloth one. Measure the width at the top, middle and bottom of the opening and record the narrowest number. Measure the height at the left, center and right and record the longest number.

Check depth as well: most roller and zebra headrails need at least 2–3 inches of usable depth for a fully recessed look.

Add overlap deliberately. We typically add 2–3 inches on each side of the opening and 3–4 inches above it, then run the shade past the sill at the bottom. That overlap is what stops light leaking around the fabric.

Confirm there is flat mounting surface where the brackets will land, and check for cranks, alarm sensors and handles that could interfere.

First, measuring the existing blinds instead of the window — old blinds may have been cut wrong. Second, rounding up on an inside mount, which produces a shade that won't fit. Third, forgetting obstructions like tile sills, alarm contacts and slider handles.

Custom shades cannot be returned for a sizing error, which is why a free professional measure is almost always the cheaper path.

Arched, angled, oversized or two-story windows should always be templated on site. So should sliding glass doors, corner windows and anything where two shades need to align visually.

Our in-home measure is free across Tampa Bay, takes about 30 minutes for a whole house, and comes with a written quote — no obligation to buy.