Inside vs. outside mount blinds: how to choose

By Opal Waverly, Painting and Window Treatment Guides Editor. Updated September 2026

What each mount looks like

An inside mount fits between the jambs of the window, so the trim around the window stays fully visible and the treatment looks built in. An outside mount is fixed to the wall or trim above the window and extends past the frame on each side, so it covers the trim and makes the window read larger.

Neither is better in general. Inside mounts suit houses with nice trim and deep frames. Outside mounts suit shallow frames, uneven windows and rooms that need darkness.

Frame depth decides first

Every blind and shade needs a minimum frame depth for an inside mount, and more still for a flush look where the treatment does not stick out. Two-inch wood and faux wood blinds need more depth than cellular or roller shades. Many mid-century and newer windows have shallow frames, and window cranks, handles and alarm sensors reduce the usable depth further.

We check depth at every window during the measure, and if a blind would stick out or hit a crank, we suggest an outside mount or a slimmer product. Our custom blinds page covers slat sizes.

Light gaps and privacy

Inside-mounted treatments leave a small gap at each side because they have to clear the jambs. In a living room nobody notices. In a bedroom, nursery or media room, those slivers of light can be the difference between dark and not dark.

An outside mount that overlaps the frame by a few inches on each side closes that gap. So does adding side channels to an inside-mounted shade. For blackout rooms we usually recommend one or the other; see cellular and roller shades for blackout options.

Out-of-square windows

Many windows, especially in older houses, are not perfectly square. An inside-mounted treatment in an out-of-square frame shows a tapering gap along one side or rubs on the other. That is why we measure width at the top, middle and bottom and height at the left, center and right.

If the measurements differ by more than a small amount, an outside mount hides the problem entirely, because the treatment is square to itself rather than to the frame.

How windows are measured for each

For an inside mount, width is measured at three points inside the frame and the narrowest is used, because the treatment has to fit at the tightest point; the manufacturer then makes a small deduction for clearance. For an outside mount, the treatment size is chosen to overlap the opening, usually a few inches on each side and above.

Measuring is where most do-it-yourself orders go wrong, and a custom treatment made to the wrong size cannot be returned. When we measure, the size is our responsibility.

Special cases

Sliding doors almost always take an outside or ceiling mount so the treatment clears the door handle; see sliding door treatments. Shutters come with their own frames that can sit inside or outside. Drapery layered over a shade usually means the shade mounts inside and the rod outside.

Bay windows can go either way, but each face is measured separately and the corners are planned so the treatments do not collide.