Quick answer: To measure for shades, first pick your mount. For an inside mount, measure the window opening width at the top, middle, and bottom and use the narrowest number, then deduct 3/8"; measure the height at three points and use the longest; and confirm you have at least 2" of frame depth for the headrail. For an outside mount, add 1–3" to each side of the width and 4–6" above the opening for full light control, and measure the height down to where you want the shade to stop. Always use a steel tape and record to the nearest 1/8".
Accurate measurements are essential when ordering shades to ensure a perfect fit and optimal functionality. The two primary mounting options are inside mount and outside mount, each with distinct advantages.
Two Primary Mounting Options:
Inside Mount:
Installing shades within the window frame offers a clean, streamlined appearance and preserves the window trim. However, it requires sufficient window depth—typically at least 2 inches—to accommodate the mounting brackets and shades. If your window depth is inadequate, consider opting for an outside mount.
Outside Mount:
Mounting shades outside the window casing can cover imperfections and provide a more substantial presence. This method is versatile and doesn't require a minimum window depth, making it suitable for various window types, including those with shallow sashes or deep window sills.
Inside vs. Outside Mount: Measuring at a Glance
| Step | Inside Mount | Outside Mount |
|---|---|---|
| Width | Measure the opening at top, middle & bottom; use the narrowest number, then deduct 3/8". | Measure across the opening and add 1–3" per side to cover the casing and block light. |
| Height | Measure at left, middle & right; use the longest number. | Measure from the mounting point to where you want the shade to stop, adding 4–6" above the opening. |
| Depth needed | At least 2" of flat frame depth for the headrail & brackets. | No minimum depth — works on shallow frames & deep sills. |
| Best for | Clean, built-in look that shows off window trim. | Maximum coverage & light block; hides uneven or shallow frames. |
Measuring for Different Mount Types:
Measuring for Inside Mount Shades:
Width: Measure the inside width of the window frame at three points—top, middle, and bottom. Use the narrowest measurement, deduct 3/8"to ensure the shade fits within the frame.
Height: Measure the inside height at three points—left, middle, and right. Use the longest measurement to ensure the shade covers the entire window height.
Depth: Measure the depth(at least 2 inches) of the window frame to confirm it can accommodate the mounting brackets and shade.
Measuring for Outside Mount Shades:
Width: Measure the desired width, extending beyond the window frame to cover the casing and allow for mounting brackets. Adding 1-3 inches to the width is recommended for optimal light control and privacy. Not adding width is ok if your frame is thick enough to keep light out.
Height: Measure from the desired top mounting point to the bottom of the window sill or the point where you want the shade to end. Adding 4-6 inches to the height above the window opening is recommended for optimal light control, and the shade headrail has its own height (especially the cordless and motorized system), making it above the window for not against your window decor frame. Or add at least 2 inches for the brackets to install.
Measuring for Bay Window:
Determine Projection (P): Mark the depth 2 to 3 inches, the shades will project from the wall in the corner angles.
Measure Center Panel: Measure the width between the two P marks in the corners of the center window.
Measure Side Panels: Measure the width of each side window, adding desired overlap only to the outermost edge of the bay. This ensures clearance.
Additional Tips:
Use a Steel Measuring Tape: For accuracy, use a steel measuring tape instead of a cloth one.
Measure to the Nearest 1/8 Inch: Precision is crucial; avoid rounding measurements.
Account for Obstructions: Identify any window hardware, handles, or obstructions that might interfere with the shade's operation.
Consider Mounting Hardware: Ensure there's sufficient space above the window for mounting brackets, especially for outside mounts.
The Shades' Headrail Size
The shade's headrail size will require inside mount frame depth and outside mount height. Please check the headrail size of different types of shades below:
Cordless Roman Shades Headrail Size:
Motorized Roman Shades Headrail Size:
No-Drilling Roman Shades Headrail Size:
Spring System Roman Shades Headrail Size:
Motorized Woven Wood Shades Headrail Size:
Cordless Woven Wood Shades Headrail Size:
No-Drill Woven Wood Shades Headrail Size:
Roller Shades Headrail Size:
Roller Shades with Cassette Headrail Size:
By the way, CURTARRA offers an easy-to-use shade measurement tool for you.
Frequently Asked Questions
How do you measure a window for roller shades?
For an inside mount, measure the opening width at the top, middle, and bottom, use the narrowest number, and deduct 3/8"; measure the height at three points and use the longest. For an outside mount, add 1–3" to each side of the width and 4–6" above the opening, then measure the height down to where you want the shade to stop. Roller shades follow the same rules as other shades — just confirm the headrail (and cassette, if you choose one) fits your frame depth.
Inside mount vs. outside mount — which should I choose?
Choose an inside mount for a clean, built-in look when your frame has at least 2" of flat depth. Choose an outside mount when your frame is shallow, uneven, or when you want maximum light block and coverage — it has no depth requirement and lets you extend the shade beyond the opening.
How much frame depth do I need for an inside-mount shade?
Plan on at least 2 inches of flat depth so the headrail and mounting brackets sit fully inside the window. Cordless and motorized systems have taller headrails — check the headrail-size diagram for your specific shade type before ordering. If you're short on depth, switch to an outside mount.
How do I measure a bay window for shades?
Mark the projection (P) 2–3" from each inside corner so the shades clear one another. Measure the center panel between the two P marks, then measure each side window, adding your desired overlap only to the outermost edge of the bay so the panels don't collide in the corners.
Should I add width for outside-mount shades?
Yes. Adding 1–3" to each side of the opening improves privacy and light control by covering the gap between the shade and the wall. You can skip the extra width only if your frame is thick enough to block light on its own.
Keep Reading
Ready to order? Every Curtarra shade is made to your exact measurements. Browse our custom roller shades collection — choose blackout, light-filtering, or solar, cordless or motorized, and order a free color-card sample before you commit.
