Use a rigid steel tape measure. Record width first, then height, in inches to the nearest 1/8 inch. Measure each window separately and check your measurements before ordering. The 1/8-inch measurement precision is separate from the 3/8-inch inside-mount width deduction described below.
Choose Your Mount Type
Inside mount: The shade fits within the window opening. Check the clear depth and any obstructions, and follow the depth requirement for your selected cellular shade model.
Outside mount: The shade mounts on the wall or trim. Confirm the planned top of the headrail and the area you want the finished shade to cover.
Inside Mount: Width
- Measure the inside width at the top, middle, and bottom.
- Use the smallest measurement; do not round it up.
- Subtract 3/8 inch once to calculate the order width.
Example: A smallest opening width of 40 inches gives an order width of 39 5/8 inches. This is the calculated order width; do not subtract another 3/8 inch from it.
Inside Mount: Height
- Measure from the top inside edge to the sill at the left, center, and right.
- Use the largest measurement as the order height.
- Do not deduct from the height.
Outside Mount: Width
Measure the full window width, including the moulding. Adding 1/2 inch in total is a starting point for planning coverage, not a requirement to add 1/2 inch to a width that already includes your chosen overlap.
Choose the left and right edges of the finished shade and measure the full distance between them. Increase overlap where needed and where space permits; for example, 1 1/2 inches per side may be considered when planning additional coverage. This is an example, not a maximum or a guarantee of complete light blocking or privacy.
Enter your final planned coverage width as the order width. Do not apply the 3/8-inch inside-mount deduction.
Outside Mount: Height
Measure from the planned top of the headrail to the desired bottom edge of the shade. Use this full distance as the order height.
The window height including the moulding plus 3 inches is a starting point for planning the headrail position and coverage. If you mount the headrail higher or extend the shade lower, measure the complete planned distance. Do not add another 3 inches after measuring that finished height.
Planning example: A window measuring 40 inches wide by 60 inches high, including the moulding, gives a starting coverage size of 40 1/2 inches wide by 63 inches high. Confirm or adjust this size for your actual headrail position, chosen overlap, and available space before ordering.
Order Size Reference
| Mount | Order width | Order height |
|---|---|---|
| Inside mount | Smallest opening width minus 3/8 inch, deducted once | Largest opening height; no deduction |
| Outside mount | Final planned coverage width, including your chosen overlap; no inside-mount deduction | Distance from the planned top of the headrail to the desired bottom edge; no additional allowance after measuring this distance |
Before You Order
- Confirm the mount type, model-specific depth, and available size limits.
- Check handles, locks, screens, and trim for obstructions.
- Record the original window measurements separately from the calculated order dimensions.
- For an inside mount, apply the width deduction once and leave the height undeducted. For an outside mount, use your final planned coverage dimensions.
- These instructions calculate order dimensions for a finished shade. They are not instructions to trim a delivered shade or cut materials for a DIY kit.
- Check what each product order field asks for. If a field requests the original window-opening measurement or its instructions differ from this guide, contact us before submitting rather than combining two sets of adjustments.
See the Cellular Shade Installation Guide. For help before ordering, email your mount type, window photos, and measurements to info@diycurtain.com.
