How to Measure for Custom Blinds and Shades: Inside vs Outside Mount

Measure the width in three places and the height in three places, then use the smallest width and the longest height for an inside mount. That one rule prevents most measuring failures. The harder question is whether the window should be an inside mount at all, and that depends on depth, squareness, and what the treatment has to do. Here is how we decide.

What is an inside mount?

The treatment sits inside the window opening, against the frame. It looks tailored, shows off the trim, and keeps the wall clean. It requires enough flat depth for the headrail, typically two to three and a half inches depending on the product, and an opening that is reasonably square.

What is an outside mount?

The treatment mounts on the wall or trim above the opening and overlaps the window on all sides. It hides an out-of-square opening, blocks far more light around the edges, and makes a small window look larger. It is the right answer more often than people expect, especially in older Denver homes.

When should you choose an outside mount?

Choose outside mount when the opening is too shallow for the headrail, when the frame is visibly out of square, when you need true blackout with no side light in a bedroom or media room, or when you want a short window to read taller. Our blackout bedroom guide explains why side light is the thing that actually wakes people up.

How do you measure for an inside mount?

Measure the exact opening width at the top, middle, and bottom, and record the narrowest. Measure the height at the left, center, and right, and record the longest. Do not subtract anything. The workroom takes the deductions. Then measure the flat depth from the front of the frame to the glass or to the first obstruction, and note any cranks, handles, or alarm contacts.

How do you measure for an outside mount?

Decide the coverage first. Add at least two inches on each side of the opening and three to four inches above for the mounting, then measure that finished rectangle. For blackout, go wider. Confirm you have flat wall or trim to anchor into across the full width, and note any crown molding or light fixtures in the way.

What tools do you need?

A steel tape measure, never a cloth one, a pencil, and a written chart with a row for every opening. Record to the nearest eighth of an inch and label each row by room and position, such as primary bedroom, west window. Photograph each opening next to your notes. Guessing at which window a number belongs to is a common and expensive error.

What are the most common measuring mistakes?

Rounding up on an inside mount, which makes the shade bind. Measuring the glass rather than the opening. Forgetting to check depth, so the headrail projects past the trim. Ignoring an obstruction like a window crank. Measuring one window and assuming a matching pair is identical, which in a Denver bungalow it usually is not.

Does the product change the measurement?

Yes. Shutters need the most depth and the most careful frame assessment, cellular shades need the least, and drapery is measured from the rod, not the opening, so the rules above do not apply to it at all. Compare products first in our shade styles guide, then measure for what you actually chose. Product pages for custom blinds and plantation shutters list depth requirements.

Should you measure yourself at all?

Measure to budget, not to order. Your numbers are perfect for getting an accurate estimate and comparing options in our Denver pricing guides. When it is time to order, we measure and carry the responsibility for the fit. The full process is described in our installation guide.

Ready for exact numbers?

Book a complimentary in-home consultation. We measure every opening, confirm the mount type window by window, and quote from real numbers. Start with our Denver window treatment services.