How to Measure Windows for Shades
Inside mount vs outside mount, width vs height, window depth, and the mistakes that cause returns.
Decide the mount first
Inside mount sits in the window casing and looks built-in. Outside mount sits on the trim or wall and covers more of the opening.
Measure after you choose a mount. The same window produces two different shopping sizes.
Width
For inside mount, measure the exact width at the top, middle, and bottom. Shop the narrowest measurement so the shade can clear the frame.
For outside mount, measure the opening and add coverage on each side — typically 1.5" to 3" total — so light doesn’t leak around the edges.
Height
Inside mount: measure left, center, and right from the top of the casing to the sill. Use the longest if you want full coverage to the sill.
Outside mount: measure from where the headrail will sit to where you want the shade to end — sill, apron, or below.
Depth
Inside-mount shades need enough casing depth for brackets. Many bamboo and Roman styles want around 1.5"–2". If the window is shallow, choose outside mount.
Exact vs nominal sizes
A shade labeled 36" is the ordering width, not always the cloth width. Manufacturers often deduct a fraction of an inch for inside-mount clearance. If you are replacing an existing shade, match the ordered size printed on the headrail tag when you can.