For inside mount, measure width at three points and use the narrowest; measure height at three points and use the longest. For outside mount, add 3–4 inches to width and 2–3 inches to height. Always use a steel tape measure and submit raw measurements without deductions.
Getting the right fit starts with accurate measurements. Whether you're ordering for a nursery, living room, or bedroom, accurate measurements are the foundation of a perfect fit. The good news: measuring correctly takes about five minutes per window if you follow the right steps. Here's exactly how to do it.
Before you measure, make sure you've already decided which type of cellular shade you want — single, double, or triple cell construction affects the headrail depth and stack height, which can influence your mount type decision. Our guide on single vs double vs triple cell honeycomb shades and their R-value insulation performance will help you choose the right construction before you order. For a more detailed measuring walkthrough with a built-in reference calculator, see our Professional Measuring Guide for Cellular Shades.
Step 1: Decide Inside Mount or Outside Mount
Inside mount gives a clean, built-in look but requires at least 1.5–2 inches of frame depth (deeper for cordless models); outside mount covers the full frame and works for any window regardless of depth.
Before you measure, choose how the shade will sit.
- Inside mount: the shade fits inside the window frame, flush with the wall. Gives a clean, built-in look. Requires at least 1.5–2 inches of depth in the frame — deeper for shades with a cordless lift mechanism.
- Outside mount: the shade mounts on the wall or trim above the window, covering the entire frame. Better if you want more light blockage, or if the frame is too shallow for inside mount.
If you're not sure which one your window supports, check the frame depth first — that decision affects how you measure everything else.
Step 2: Measure for Inside Mount
Use a steel tape measure; take three width measurements and use the narrowest, and three height measurements and use the longest — do not round up or add any deductions.
Use a steel tape measure, not fabric — it won't sag or give an inaccurate reading.
Width
- Measure the width at the top, middle, and bottom of the window opening.
- Use the narrowest of the three measurements. Frames are rarely perfectly square.
- Do not round up or add anything — we account for mounting clearance on our end.
Height
- Measure the height at the left, center, and right of the opening.
- Use the longest of the three measurements, so the shade fully covers the window when extended.
Depth
Check that your frame has at least 1.5–2 inches of depth for the headrail to sit without hitting the window handle or sill — deeper for cordless models.
Step 3: Measure for Outside Mount
For outside mount, add 3–4 inches total to the opening width (1.5–2 inches per side) and 2–3 inches to the height for the mounting bracket — more overlap means better light blockage.
Width
Measure the width of the area you want covered, then add 3–4 inches total (1.5–2 inches on each side) so the shade overlaps the frame and blocks light gaps.
Height
Measure from where you plan to mount the headrail down to the sill or desired stopping point, then add 2–3 inches at the top for the mounting bracket.
Common Measuring Mistakes to Avoid
The four most common mistakes are rounding measurements, measuring only once, forgetting to check frame depth, and using a fabric tape measure — any one of these can result in a shade that doesn't fit.
- Rounding measurements. Even a quarter inch matters for a snug inside-mount fit.
- Measuring only once. Windows settle over time and are often not perfectly square — always take three measurements per dimension.
- Forgetting mounting depth. A shade ordered for inside mount won't work if your frame is too shallow — outside mount is the fix.
- Using a fabric tape measure. It stretches slightly, which throws off small windows especially.
Quick Reference
Inside mount: use narrowest width and longest height. Outside mount: add 3–4 inches to width and 2–3 inches to height above the opening.
| Mount Type | Width Rule | Height Rule |
|---|---|---|
| Inside mount | Use narrowest measurement | Use longest measurement |
| Outside mount | Add 3–4" total to opening width | Add 2–3" above opening for bracket |
Still Not Sure?
If your window has an unusual shape or shallow frame, send your measurements and a photo to support@uamblinds.com and we'll verify before your order goes into production.
While you're planning your order, it's also worth thinking about UV protection — the fabric you choose affects how much UV reaches your furniture and flooring. Our guide on which window treatments actually protect your furniture from UV fading explains how openness factor and fabric type determine UV blockage, so you can choose the right shade for both fit and protection.
If your window has an unusual shape, a shallow frame, or you're just not confident measuring solo, send us your measurements and a photo at support@uamblinds.com — we'll double check before your order goes into production.
Every UAM Blinds shade is factory direct and made to your exact size, starting at $47.99, with free shipping on orders over $99.
Further Reading
- Professional Measuring Guide for Cellular Shades (2026) — deeper guide with frame depth requirements and reference calculator
- Single vs Double vs Triple Cell Honeycomb Shades: R-Value Compared — choose the right construction before you measure
- TDBU vs. Standard Cellular Shades — understand operating systems before ordering
- Blackout vs Light Filtering Blinds — choose the right fabric before you measure
- How to Install TDBU Cellular Shades — installation guide after measuring
- Which Window Treatments Actually Protect Your Furniture From UV Fading? — choose the right fabric for UV protection before you order
Frequently Asked Questions
Do I measure the glass or the window frame opening?
Always measure the frame opening — the visible recessed area inside the trim — not the glass itself. The glass is always smaller than the opening and will result in an undersized order.
Should I subtract anything from my measurements before ordering?
No. Submit your raw measurements exactly as taken. UAM Blinds handles all necessary production deductions on our end — submitting pre-deducted numbers is one of the most common causes of incorrectly sized orders.
What if my three width or height measurements are different?
That's normal — most window frames are not perfectly square. For inside mount, use the narrowest width and the longest height. If measurements differ by more than 1/4 inch, consider outside mount, which is more forgiving of irregular frames.
How much overlap should I add for outside mount?
Add 3–4 inches total to the width (approximately 1.5–2 inches per side) and 2–3 inches to the height for the mounting bracket. More overlap provides better light blockage and a more finished look.