Blinds are one of the few things you really can’t return once they’re cut to size — so measuring correctly the first time saves you money and frustration. The good news: it takes about five minutes and one tool you already own.
The whole job comes down to a single decision made up front: inside mount or outside mount?
Inside mount vs. outside mount
- Inside mount sits inside the window frame, for a clean, built-in look. It needs enough depth in the frame for the blind to fit. Best when you have a deep frame and attractive trim you want to show off.
- Outside mount is installed on the wall or trim above and around the window. It makes windows look larger, hides an off-square frame, and works when the frame is too shallow for an inside mount.
Decide this first, because the two are measured in opposite ways: inside mount measures the opening; outside mount measures the area you want to cover.
What you’ll need
- A steel tape measure (not cloth — fabric tapes stretch)
- A pen and paper
- 60 seconds per window
Always measure to the nearest ⅛ inch, and write width before height (W × H) — it’s the industry standard, and mixing them up is the #1 ordering error.
How to measure for an inside mount
- Measure the width in 3 places — top, middle, and bottom of the window opening. Use the narrowest measurement.
- Measure the height in 3 places — left, center, and right. Use the tallest measurement.
- Measure the depth of the frame to be sure it’s deep enough for the blind you want (the product page lists the minimum depth).
- Do not make any deductions. The factory takes the small fit allowance for you — just report the exact opening.
How to measure for an outside mount
- Decide your coverage. For privacy and light control, add at least 3 inches on each side (6 inches total) to the window width, and overlap the top by 3+ inches.
- Measure the total width you want the blind to cover.
- Measure the total height, from where the headrail will sit down to where you want the blind to end (sill, or below it).
- Make sure there’s flat wall or trim to mount the brackets.
Common measuring mistakes
- Using a cloth tape (it stretches — readings come out long).
- Reversing width and height. Always W × H.
- Making your own deductions on inside mounts — that’s what causes blinds to come out too narrow.
- Forgetting to check frame depth before choosing an inside mount.
Frequently asked questions
Should I get inside or outside mount blinds?
Inside mount for a clean, built-in look when the frame is deep enough. Outside mount to make a window look bigger, cover a shallow or out-of-square frame, or maximize light blocking.
Do you deduct anything when measuring inside-mount blinds?
No. Report the exact window-opening measurements — the manufacturer makes the small deduction for a proper fit automatically.
How do I measure if my window isn’t square?
Measure width in three spots and use the narrowest; measure height in three spots and use the tallest. If it’s badly out of square, an outside mount hides it better.
What’s the most common mistake when measuring for blinds?
Reversing width and height, and using a stretchy cloth tape. Always use a steel tape and record width first.
Get the perfect fit — guaranteed
Measuring is straightforward, but if your windows are oddly shaped, extra-wide, or you just want a second set of eyes, we’re happy to help.
👉 Shop made-to-measure blinds, or book a free consultation and we’ll measure and recommend the right mount for every window.