Small and odd-shaped windows

Arches, angle-tops, skylights and slim sidelights: what to measure and what to buy.

A woman works at a home office table with her dog at her feet, a light-filtering roller shade softening the window light

Short answer: on small windows, an outside mount can make the window look bigger.^{[1 · Oct 29, 2026]}^{[2 · Oct 29, 2026]} Shaped windows such as arches and angle-tops have their own measuring rules; for an outside mount, Blinds.com adds 2 in to the measurements.^{[3 · Oct 29, 2026]}

Small and narrow windows

Outside mount makes a small window look larger and hides plain trim.^{[1 · Oct 29, 2026]}^{[2 · Oct 29, 2026]}
Smaller slats suit narrow windows and French doors with little depth.^{[4 · Oct 29, 2026]}
Tall, narrow windows usually look best with horizontal blinds.^{[5 · Oct 29, 2026]} So do smaller and narrower windows that open up and down.^{[6 · Oct 29, 2026]}
Check the minimum width for the product and control you want. Minimum sizes vary by brand and lift. {UNV}

Door windows and French doors

Blinds sealed between panes of glass ("enclosed" door blinds) are one option for doors.^{[6 · Oct 29, 2026]} Smaller slats work better on doors with little depth.^{[4 · Oct 29, 2026]}

Arched windows

Blinds.com describes several arch shapes: a perfect half circle (its height is half its width), a taller Palladian arch, a flatter eyebrow arch, an elongated arch and a quarter arch.^{[3 · Oct 29, 2026]} An inside mount on an arch needs at least 1½ in of depth and 2¼ in to sit fully recessed.^{[3 · Oct 29, 2026]} For an outside mount, add at least 2 in to your measurements.^{[3 · Oct 29, 2026]}

Angle-top windows

For an outside mount on an angle-top window, add 2 in to each final measurement.^{[3 · Oct 29, 2026]} For inside mounts, follow the brand's own measuring sheet for the shape.

Skylights

Measure the diagonals. If they differ by ¼ in or more, the skylight is out of square and Blinds.com requires an outside mount.^{[3 · Oct 29, 2026]}

Out-of-square windows

The same goes for ordinary windows: if your two diagonal readings aren't equal, Home Depot's guide recommends an outside mount.^{[7 · Oct 29, 2026]} Outside mounts handle non-square windows better.^{[2 · Oct 29, 2026]}

Windows with cranks or handles

Casement cranks and latches can get in the way of an inside mount.^{[2 · Oct 29, 2026]} Measure your depth to the first thing that sticks out.^{[3 · Oct 29, 2026]} For outside mounts, extension brackets can bring the blind forward; Levolor's vertical blind brackets extend 2 to 4 in.^{[1 · Oct 29, 2026]}^{[8 · Oct 29, 2026]}

Sources: 1. Levolor, How to measure windows for blinds and shades. 2. Bali, Cellular and pleated shades measuring guide (PDF). 3. Blinds.com, How to measure. 4. Levolor, Real wood vs. faux wood blinds. 5. Hunter Douglas, Buyer's guide to window blinds. 6. The Home Depot, Blinds category and buying notes. 7. The Home Depot, Measuring the right way for window treatments (PDF). 8. Levolor, Vertical blinds technical guide (PDF). Checked Oct 29, 2026. Trademarks belong to their owners; figures are restated in our own words and tables, not reproduced.