Calculator + chartEnter your measurements below and it works the answer out.
Inside mount: measure the opening in three places each way and order the narrowest width and the tallest height. Outside mount: add 3 inches each side and above. Enter your numbers and the calculator gives the size to order.
| Blind type | Flush mount (fully inside) | Minimum mount |
|---|---|---|
| Roller shade | 2½ in | 1½ in |
| Cellular / honeycomb | 2 in | 1 in |
| Faux wood 2 in slats | 3 in | 1½ in |
| Real wood 2 in slats | 3 in | 1½ in |
| Vertical blind | 3½ in | 2 in |
| Roman shade | 3 in | 1½ in |
Less than the minimum: mount outside. Between minimum and flush: the blind works but sticks out past the frame.
Inside mount. The blind must clear the frame at its narrowest point, so the order width is the smallest of the three widths, and the order height is the largest of the three heights so it reaches the sill everywhere. Give the exact measurement; the factory takes its own ¼ to ½ inch deduction for clearance — do not deduct yourself, or the blind will have gaps on both sides.
Outside mount. The blind should cover the opening and overlap the wall to block light: 1½ to 3 inches past each side (the calculator uses 3, so 6 inches added to the widest width) and 3 inches above the frame, plus the height of the opening. Order the width as the exact overall size — there is no factory deduction on outside mounts.
Depth check. An inside mount needs a frame deep enough for the headrail; the table gives the minimum for each type. Measure from the glass (or the window's inner stop) to the front edge of the frame.
Inside the frame for an inside mount (the blind sits in the recess), outside on the trim or wall for an outside mount. Inside looks cleaner; outside blocks more light and hides an out-of-square window.
No. Send the exact narrowest width; the manufacturer deducts ¼–½ inch so the blind clears the frame. If you deduct as well, the blind ends up with light gaps.
3 inches wider on each side of the opening (6 inches total) is the usual figure; 1½ inches is the minimum. Add 3 inches above for the headrail.
Window frames are rarely square. An inside blind must fit the narrowest point or it will not go in; an outside blind must cover the widest point.