Blinds that fit, first time

What size blinds do I need?

Type in your window measurements and get the width and height to order, for inside or outside mount, using the measuring rules blind brands publish. Every rule links to its source.

Size my blinds How to measure

Inches and cm
Sources on every rule
No sign-up

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

Blind size calculator

Measure to the nearest ⅛ in. Results update as you type.

Mount

InsideOutside

What are you buying?

Units

inchescm

Width in 3 places (top, middle, bottom): we use the narrowest

Top

Middle

Bottom

Height in 3 places (left, center, right): we use the longest

Left

Center

Right

Recess depth front of frame to glass or first obstacle

Shortest depth reading

Diagonals optional squareness check

Corner to corner

Other way

Type inches as 34, 34.5, 34 3/8 or 34-3/8.

Turn on JavaScript to use the calculator, or follow the step-by-step sizing guide.

A cross-check based on published brand measuring rules, not a guarantee of fit. Brands differ; follow the instructions for the product you order.

The 3-point rule

Measure three times, order once

3 widthstop, middle and bottom; order the narrowest for inside mount^{[1 · Oct 29, 2026]}^{[2 · Oct 29, 2026]}

3 heightsleft, center and right; order the longest (verticals: shortest)^{[1 · Oct 29, 2026]}^{[3 · Oct 29, 2026]}

⅛ inmeasure to the nearest eighth with a steel tape^{[1 · Oct 29, 2026]}^{[4 · Oct 29, 2026]}

No deductionsthe factory takes them on inside mounts^{[1 · Oct 29, 2026]}^{[4 · Oct 29, 2026]}

Step-by-step measuring guide · Deductions explained

Common window sizes

Window size codes, decoded

Drawn to scale. Codes are width then height in feet and inches.^{[5 · Oct 29, 2026]}

A 2840 window is 2 ft 8 in by 4 ft 0 in, or 32 × 48 in.^{[5 · Oct 29, 2026]} The code may describe the rough opening, so always measure the frame itself.^{[5 · Oct 29, 2026]} Standard window and blind sizes chart

Friends share dinner around a wooden table in front of windows dressed with linen roman shades

Inside or outside?

Pick your mount first

Inside mount is the most popular; it needs enough frame depth.^{[1 · Oct 29, 2026]}
Outside mount makes windows look larger and controls light better.^{[1 · Oct 29, 2026]}
Out-of-square frame? Home Depot's guide recommends outside mount.^{[4 · Oct 29, 2026]}

Inside vs outside mount · Blind types and depths

Depth check

How deep does the frame need to be?

Cellular and roman shades
½ in to mount inside; 2⅛ in to sit flush.^{[1 · Oct 29, 2026]}
Faux and real wood, 2 in
¾ in to mount inside; 2½ in to sit flush.^{[1 · Oct 29, 2026]}
Roller and solar shades
1½ in to mount inside; 2½ in to sit flush.^{[1 · Oct 29, 2026]}
Metal mini blinds, 1 in
½ in to mount inside; 1 13/16 in to sit flush.^{[1 · Oct 29, 2026]}
Vertical blinds
2½ in to mount inside; 3 in for the headrail to sit flush.^{[3 · Oct 29, 2026]}
Not enough depth?
Go outside mount.^{[2 · Oct 29, 2026]} All types

A dad, his son and a beagle stand at a sliding patio door with light gray vertical blinds stacked to one side

Patio doors

Sliding glass doors

Vertical blinds and panel tracks suit large windows and sliding doors.^{[6 · Oct 29, 2026]}^{[7 · Oct 29, 2026]}
Overlap at least 4 in each side, mount at least 3 in above, and take ½ in off at the floor.^{[3 · Oct 29, 2026]}
Stack the vanes on the side away from the opening.^{[8 · Oct 29, 2026]}

Blinds for sliding glass doors

A grandmother and granddaughter read together on a bay window seat with a white cellular shade on each of the three windows

Bays and bows

Bay windows without the corner clash

One blind and headrail per window.^{[9 · Oct 29, 2026]}
Where windows meet, mark the corners with cardboard squares as deep as the blind, then measure between the marks.^{[10 · Oct 29, 2026]}

Bay window blinds · Small and odd-shaped windows

A dad plays with building blocks on the floor with his toddler beside a window fitted with a cordless beige cellular shade

Little ones at home

Go cordless

Young children can strangle on window covering cords in moments, even with an adult nearby. The CPSC says cordless is the safest choice.^{[11 · Oct 29, 2026]}

Cordless blinds and child safety · Custom vs ready-made

Guides

Everything about sizing blinds

Sources: 1. Levolor, How to measure windows for blinds and shades. 2. Blinds.com, How to measure. 3. Levolor, Vertical blinds technical guide (PDF). 4. The Home Depot, Measuring the right way for window treatments (PDF). 5. Pella, Standard window sizes. 6. Levolor, The quick-start guide to choosing blinds and shades. 7. The Home Depot, Blinds category and buying notes. 8. Levolor, Vertical blinds side-stack installation instructions (PDF). 9. Bali, Wood, composite and faux wood blinds measuring guide (PDF, hosted by a retailer). 10. Blinds.com, How to measure for a bay window. 11. US Consumer Product Safety Commission, Go cordless. Checked Oct 29, 2026. Trademarks belong to their owners; figures are restated in our own words and tables, not reproduced.