What size blinds do I need?

Your tape measure gives you six numbers. Here's how they become the one size you order.

Parents, two children and a golden retriever laugh together on a sofa in a sunny living room with white faux wood blinds on the windows

Short answer: for an inside mount, order the exact narrowest width and longest height of the opening, and let the factory take its small deduction.^{[1 · Oct 29, 2026]}^{[2 · Oct 29, 2026]}^{[3 · Oct 29, 2026]} For an outside mount, order the area you want covered plus overlap on each side, plus room above for the headrail.^{[1 · Oct 29, 2026]}^{[2 · Oct 29, 2026]}^{[4 · Oct 29, 2026]} The calculator does this for you.

Worked example: inside mount

A double-hung window, faux wood blinds. Your readings:

Width	Reading	Height	Reading
Top	34¼ in	Left	59⅞ in
Middle	34⅛ in	Center	60 in
Bottom	34 3/16 in	Right	59 15/16 in

Width: the narrowest is 34⅛ in. Order that. A blind made to the 34¼ in top reading would bind at the middle.^{[1 · Oct 29, 2026]}^{[2 · Oct 29, 2026]}
Height: the longest is 60 in. Order that.^{[1 · Oct 29, 2026]}^{[2 · Oct 29, 2026]} (If the longest had been 59 15/16, Blinds.com and SelectBlinds would have you round up to 60, while Home Depot's guide rounds down to 59⅞.^{[2 · Oct 29, 2026]}^{[5 · Oct 29, 2026]}^{[3 · Oct 29, 2026]})
Order: 34⅛ × 60 in (86.7 × 152.4 cm), inside mount. Don't subtract anything.^{[1 · Oct 29, 2026]}^{[3 · Oct 29, 2026]}
Depth: 2 in faux wood needs ¾ in to mount inside and 2½ in to sit flush.^{[1 · Oct 29, 2026]}

Worked example: outside mount

Same window, but the trim measures 38 in across and you want the blind to cover it, from 3 in above the trim down to the sill, 63 in in all.

Brand's overlap rule	Width to order
At least ¾ in per side (Levolor)^{[1 · Oct 29, 2026]}	39½ in
1½ in per side (Bali, Home Depot)^{[6 · Oct 29, 2026]}^{[3 · Oct 29, 2026]}	41 in
At least 2½ in per side (Blinds.com)^{[2 · Oct 29, 2026]}	43 in

Overlap helps with light control and privacy.^{[3 · Oct 29, 2026]} Then check the wall: Home Depot asks for at least 2 in of flat surface above the frame for brackets, and Blinds.com suggests at least 3 in.^{[4 · Oct 29, 2026]}^{[2 · Oct 29, 2026]} Outside-mount blinds are made to exactly what you order.^{[2 · Oct 29, 2026]}^{[7 · Oct 29, 2026]}

The rules in one table

	Inside mount	Outside mount
Width	Narrowest of top, middle, bottom^{[1 · Oct 29, 2026]}	Area to cover + overlap both sides^{[1 · Oct 29, 2026]}
Height	Longest of left, center, right^{[1 · Oct 29, 2026]}	Headrail position to sill or stop point^{[1 · Oct 29, 2026]}
Vertical blinds	Width at the top; shortest height^{[8 · Oct 29, 2026]}	At least 4 in overlap per side; 3 in above^{[8 · Oct 29, 2026]}
To the floor	n/a	Take off ½ in for clearance^{[3 · Oct 29, 2026]}^{[8 · Oct 29, 2026]}
Who deducts	The factory^{[1 · Oct 29, 2026]}^{[3 · Oct 29, 2026]}	Nobody^{[2 · Oct 29, 2026]}

Stock sizes

Buying ready-made? Pick a size close to your opening, then have it cut, or choose an outside mount and a size that covers it. Home Depot's associates cut blinds bought in store to size for free.^{[4 · Oct 29, 2026]} See custom vs ready-made blinds.

Sources: 1. Levolor, How to measure windows for blinds and shades. 2. Blinds.com, How to measure. 3. The Home Depot, Measuring the right way for window treatments (PDF). 4. The Home Depot, Blinds category and buying notes. 5. SelectBlinds, How to measure for custom blinds and shades. 6. Bali, Wood, composite and faux wood blinds measuring guide (PDF, hosted by a retailer). 7. Bali, Cellular and pleated shades measuring guide (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.