Get It Right the First Time: Your Foolproof Guide to Measuring for Cellular Shades

Ordering new cellular shades should be exciting, not stressful. The key to that perfect, professional-looking installation isn't a secret—it's accurate measurement. A shade that's even a quarter-inch off can rattle in the frame, let in light gaps, or simply not fit. The good news? With the right tools and a methodical approach, measuring for cellular blinds is a straightforward DIY task anyone can master. Let's walk through the process so you can order with complete confidence.

Before you even grab your tape measure, you need to make a crucial decision: inside mount or outside mount. This choice will dictate every measurement you take and dramatically affect the final look of your window. An inside mount, where the shade sits neatly within the window frame, offers a clean, built-in appearance. An outside mount, where the shade brackets are installed on the wall or molding above and outside the frame, can make a window appear larger and is ideal for frames that are shallow, uneven, or lack a deep enough recess.

Gathering Your Toolkit

You don't need much. A sturdy steel tape measure is non-negotiable—avoid cloth or flexible tapes as they can sag and give inaccurate readings. A notepad and pen to record each measurement clearly, labeling them by window and specifying width and height, is essential. A small level can be handy for checking if your window frame is perfectly square, which they often are not. That's why we measure in multiple places.

The Inside Mount Method

For an inside mount, you're measuring the recessed space where the shade will live. Start with the width. Measure the exact distance from the left inside edge of the frame to the right inside edge. Do this at the top, middle, and bottom of the window opening. Jot down all three numbers. The manufacturer will use the smallest of these three width measurements. This ensures your shade won't rub against the frame or get stuck. If your window is out of square, using the smallest number guarantees a proper fit.

Next, measure the height. Place your tape measure at the top inside edge of the frame and run it down to the windowsill. Again, take three measurements: at the left side, the center, and the right side. Record all three. Here, you'll provide the manufacturer with the largest of these three height measurements. This makes certain the shade will be long enough to cover the entire opening. Most manufacturers will then deduct a small amount (typically 1/4 inch or so) from your provided width to ensure operational clearance, but they rely on your accurate raw measurements to do that correctly.

The Outside Mount Method

Choosing an outside mount gives you more control over light blockage and perceived window size. For the width, decide how much overlap you want on each side of the window frame to prevent light seepage. A common recommendation is to add at least 1.5 to 3 inches to the total width of the window frame or glass area. Measure the exact area you want the shade to cover from left to right. This is the finished width you'll order.

For the height, measure from where you plan to mount the top bracket (usually about 1.5 to 3 inches above the frame) down to where you want the bottom of the shade to fall. This could be just below the windowsill, to the apron, or even to the floor for a dramatic effect. I learned this lesson myself in an old home with crooked windows. Trying to force an inside mount was a lesson in frustration. Switching to an outside mount not only solved the fit issue but also made the room feel taller because I mounted the brackets high above the frame.

Avoiding Common Pitfalls

Always measure each window individually, even if they look identical. Homes settle, and frames can vary. Don't assume your windows are perfectly square or level—measuring in three places is your safeguard. Use inches and measure to the nearest 1/8th of an inch for precision. Double-check your written numbers before you finalize your order. It's a simple step that can save you weeks of hassle and return shipping costs. Remember, you are measuring the window, not any old blinds or shades currently hanging.

Final Checks Before You Order

Review the measurement guidelines provided by the specific company you're ordering from. While the principles are universal, some may have small variations in their requirements. Ensure you've clearly marked which measurements are for width and which are for height, and specified “inside mount” or “outside mount” for each window. Taking a few extra minutes to verify your work is the final, most important step in the process. Accurate numbers are the only path to shades that operate smoothly, look custom-made, and provide the insulation and light control you're expecting from their honeycomb design.

Frequently Asked Questions

What if my inside mount depth is very shallow?
Most cellular shades require a minimum inside depth for the brackets and the folded shade. If your frame is less than 2 inches deep, consult the manufacturer's specs. You may need to choose a slim-profile shade or default to a secure outside mount, which has no depth restriction.

Should I measure with the existing blinds or curtains still up?
No. Always remove any existing window treatments to get measurements directly from the window frame itself. Old hardware can obstruct your tape and lead to incorrect numbers.

How do I measure for a window with a crank handle?
For casement windows with a crank, an outside mount is almost always the best solution. Measure for the outside mount, ensuring the shade's width will cover the glass area completely, and confirm the projected shade will clear the handle when it's turned.