How to Measure for Roller Shades | Window Treatments by Grace

Before You Start

You will need:

  • A steel tape measure (never a cloth or sewing tape, since they stretch and flex)
  • A pencil and paper, or your phone's notes app
  • 5 minutes per window

Record every measurement in inches, to the nearest 1/8". Do not round up or down to the nearest inch. Custom shades are made to the exact size you give us, and half an inch is the difference between a perfect fit and a shade that will not sit in the frame.

Measure every window separately, even if they look identical. Windows that appear to match are often off from each other by 1/4" or more.

Inside mount versus outside mount roller shades compared side by side. Inside mount sits within the window opening for a clean built-in look, outside mount covers the frame for maximum light blockage.

Step 1: Choose Your Mount Type

Inside Mount

The shade fits inside the window opening, flush with the wall for a clean, built-in look.

Choose inside mount if:

  • Your window frame is deep enough for the cassette headrail to sit flat inside the opening. Not sure? Send us a photo of your window before you order and we will confirm it for you.
  • You want to show off attractive window trim
  • Nothing (cranks, handles, alarm sensors) sticks out into the opening

Keep in mind: an inside mount shade always has a small light gap along each edge. That is normal and unavoidable. If total darkness matters (bedrooms, nurseries), consider an outside mount even with blackout fabric.

Outside Mount

The shade mounts on the wall or trim above the window and overlaps the opening.

Choose outside mount if:

  • Your frame is too shallow for inside mount
  • You want maximum light blockage (the overlap covers the light gaps)
  • Your window is out of square, or has obstructions in the opening
  • You want the window to appear larger

How to measure width for an inside mount roller shade. Measure the window opening at the top, middle, and bottom, then use the narrowest width.

Step 2: Measure for an Inside Mount

Width

Measure the opening width in three places: top, middle, and bottom.

Use the narrowest of the three measurements, and order that exact width. Do not subtract anything yourself. The factory automatically makes a small standard deduction (1/4") so the shade operates smoothly without rubbing the frame. If you deduct too, the gaps double.

How to measure height for an inside mount roller shade. Measure the window opening at the left, center, and right, then use the longest height.

Height

Measure the opening height in three places: left side, center, and right side.

Use the longest of the three measurements and order that exact height. No deductions needed. The factory builds in extra fabric so the shade fully reaches the sill.

Depth

Measure from the glass to the front edge of the frame and write it down. The cassette headrail needs enough flat, unobstructed depth to mount inside the opening. If your frame is shallow, or you are not sure it qualifies, send us your depth measurement and a window photo before ordering, or simply choose an outside mount, which works on any window.

Step 3: Measure for an Outside Mount

Outside mount shades are made exactly to the size you order, with no factory deduction, so the overlap is up to you.

Width

Measure the width of the area you want covered: the window opening plus any trim.

Add 2 to 3 inches to that width so the shade overlaps the frame and blocks light around the edges. Before finalizing, check for anything the shade would bump into at that width, such as light switches, door handles, or adjoining trim, and adjust if needed. For blackout shades in bedrooms, use the higher end of the range.

Order this total width.

Height

Measure from the top of the window frame down to the sill (or 2 to 3 inches below the opening if there is no sill). Order this height. The factory automatically adds extra length to account for the shade mounting above the window frame, so you will never come up short.

If you want a longer drop, for example down to the floor, simply order the full length you want covered.

Common Mistakes We See Constantly

  1. Deducting for clearance yourself on an inside mount. The factory already does this. Give us the exact opening size.
  2. Measuring only once. Openings are never square. Three measurements per dimension, always.
  3. Assuming two windows are the same size. Measure every window.
  4. Rounding to the nearest inch. Give us the nearest 1/8".
  5. Mixing up width and height. Always write measurements as Width x Height. A 36 x 72 shade and a 72 x 36 shade are very different products, and we cannot accept returns on custom items.
  6. Measuring an old shade instead of the window. Old shades were already deducted for clearance, so using their dimensions compounds the deduction and leaves big gaps.
  7. Using a cloth tape measure. Steel tape only.
  8. Ignoring obstructions. Check for window cranks, handles, alarm sensors, and light switches before choosing your mount and width.

Still Not Sure?

Measuring wrong on a custom, non-returnable product is an expensive mistake, so if you are uncertain, ask us first. Send a photo of your window with your measurements through our contact page and we will double check everything before you order. We have been measuring and installing window treatments for over 18 years.