Quick answer: Before you measure, decide whether you're doing an inside mount (shade fits within the window frame) or an outside mount (shade hangs on the wall above and around the frame). Inside mount needs precise width and height measurements of the recess itself; outside mount needs measurements that extend several inches beyond the frame on each side. Getting this decision right first is what makes the rest of the measuring process straightforward instead of confusing.
In this guide
- Why the mount decision has to come before you pick up a tape measure
- Step-by-step measuring instructions for both inside and outside mount
- The frame depth requirement that matters most if you're considering a no-drill shade
- Common measuring mistakes that lead to returns or a poor fit
- Answers to frequently asked measuring questions
Step 1: Decide Between Inside Mount and Outside Mount First
This is the decision that determines everything else about how you measure, so it's worth settling before any tape measure comes out.
Inside mount means the shade sits recessed within the window frame itself, flush with the surrounding wall. It gives a clean, built-in look and is the more common choice when the frame is deep enough to support it.
Outside mount means the shade mounts on the wall or trim above and around the window, rather than inside the recess. This is the right call when the frame is too shallow for an inside mount, when you want to make a window look larger, or when you need to cover more of the wall for better light-blocking or privacy coverage.
As a rule of thumb: if your frame depth is at least 1½–2 inches deep and you like a streamlined, recessed look, inside mount is usually the better fit. If the frame is shallow, oddly shaped, or you specifically want the shade to cover beyond the window opening, go with outside mount.
Inside Mount vs. Outside Mount, At a Glance
| Factor | Inside Mount | Outside Mount |
|---|---|---|
| Minimum frame depth needed | 1½–2 inches | Not applicable — mounts on the wall |
| Look | Clean, recessed, built-in | Makes window appear larger, more coverage |
| Measurement style | Exact recess width/height, narrowest and longest points | Window width plus 3-4 inches overlap per side |
| Best for | Deep, square frames | Shallow frames, or when more light-blocking coverage is wanted |
Step 2: Measuring for an Inside Mount
- Measure the width at three points — top, middle, and bottom of the window recess — using a steel tape measure for accuracy. Record the narrowest of the three measurements, since window frames are rarely perfectly square.
- Measure the height at three points — left side, center, and right side of the recess — from the top of the opening down to the sill. Record the longest of the three measurements.
- Check the frame depth, measuring from the front of the frame back to where the mounting hardware would sit. This matters for confirming the shade's hardware will actually fit inside the recess without protruding.
- Note any obstructions inside the recess — a crank handle, an uneven sill, or interior trim — that could interfere with the headrail or the fabric stack when raised.
Step 3: Measuring for an Outside Mount
- Measure the exact width of the window opening first, the same way you would for an inside mount, as your baseline reference.
- Add coverage on each side. A general guideline is 3-4 inches of overlap on each side beyond the frame, which helps block light gaps at the edges and makes the window appear wider. Adjust based on how much coverage you want.
- Measure the height from where you plan to mount the hardware down to where you want the shade to end — typically a few inches above the top of the frame, down to the sill or slightly past it, depending on the look you want.
- Confirm your wall surface can support the mounting hardware at the height and width you've measured, checking for any obstructions like outlets, trim, or nearby fixtures.
The Frame Depth Rule That Matters Most for No-Drill Shades
If you're considering a no-drill, tension-mounted shade, frame depth isn't just a preference — it's a functional requirement. These mounts typically need a minimum frame depth of around 1⅝ inches, with 2 inches or more recommended for a secure, long-term fit. Measure this before anything else if a no-drill mount is part of your plan, since a frame that's too shallow won't hold the tension system reliably regardless of how well the rest of the measurements are taken.
Don't Forget: Stack Height and Fold Style Affect Your Measurements Too
Beyond the mount type, one detail that trips people up is forgetting to account for how much space the fabric will take up once raised. As covered in our guide to Roman shade fold styles, a raised shade stacks several inches of fabric at the top — generally 6 to 10 inches depending on window height and fold style. If your window is on the shorter side, or if there's minimal clearance above the frame, it's worth measuring that clearance separately and factoring it into your final height decision, particularly for an inside mount where that stack space is more constrained.
Common Measuring Mistakes
- Measuring only once, at one point. Window frames are rarely perfectly square — always measure width and height at multiple points and use the narrowest width and longest height, as covered in Step 2.
- Using a cloth tape measure instead of a steel one. Cloth tape measures can stretch slightly, which introduces small errors that add up over a full window width.
- Forgetting to check frame depth before choosing inside mount. This is the single most common cause of ordering the wrong mount type — always confirm depth before deciding, not after.
- Not accounting for stack height on shorter windows. As covered above, this can result in a shade that blocks more of the usable glass than expected once raised.
- Rounding measurements instead of recording them exactly. Custom shades are built to the measurement provided — rounding up or down by even a quarter inch can affect fit, especially for inside mount.
Frequently Asked Questions
What tools do I actually need to measure accurately? A steel tape measure, a pencil and paper (or a phone note) to record each measurement immediately, and ideally a small step stool for reaching the top of taller windows safely.
Should I measure in inches or millimeters? Most custom window treatment orders in the U.S. are measured in inches, typically to the nearest eighth of an inch for the most accurate custom fit.
What if my window frame isn't perfectly square? This is common, not a sign of a problem with your window — it's exactly why Step 2 recommends measuring at three points and using the narrowest width and longest height, which accounts for minor frame irregularities.
Can I switch from outside mount to inside mount later if I change my mind? Not with the same shade — the measurements and hardware are specific to the mount type ordered, so switching means remeasuring and ordering a new shade rather than adjusting the existing one.
Do I need professional help to measure, or can I do it myself? Most people can measure accurately themselves by following the steps above carefully — professional measuring services exist mainly for unusually shaped windows, very large openings, or situations where you'd simply rather not do it yourself.
Final Thoughts
The single most important step in this whole process happens before you touch a tape measure: deciding between inside and outside mount. Once that's settled, the actual measuring is a straightforward, repeatable process — three width points, three height points, and a frame depth check if a no-drill mount is part of the plan. Taking the extra few minutes to measure carefully at this stage is what stands between a shade that fits exactly right and one that needs to be reordered.
