Choosing the Right Window Blind Size
Window blind sizing requires precise measurements to ensure proper fit, light control, and privacy. Blinds that are too narrow leave gaps that allow light leakage and reduce privacy, while oversized blinds cannot be installed or may interfere with window operation. Standard blind sizes accommodate most residential windows, but custom sizing is often necessary for non-standard openings. Understanding the difference between inside and outside mounting is essential for accurate measurement and ordering.
Blind dimensions include width, measured across the headrail from end to end, and length, measured from the top of the headrail to the bottom of the slats or fabric. Width determines how much of the window opening the blind covers horizontally, while length controls vertical coverage. For inside mounts, blinds fit within the window frame, requiring deductions from actual measurements to ensure clearance. Outside mounts cover the entire window frame and surrounding wall, requiring additions to measurements for proper overlap and light blocking.
History and Standards in Window Blind Sizing
Window blinds originated in the 18th century as adjustable slatted shutters for light control. Early blinds were custom made for each window, with no standardization. As window manufacturing standardized in the early 20th century, common window sizes emerged, leading blind manufacturers to offer standard sizes. By the 1950s, residential construction used modular window dimensions based on 2 inch increments, and blind manufacturers adopted matching size ranges.
Modern standard blind widths typically range from 18 to 108 inches in 1 inch increments for custom orders, with stock sizes available in common widths like 23, 27, 31, 35, and 39 inches. Lengths follow similar patterns, with stock sizes at 36, 48, 60, 64, and 72 inches. There is no universal regulatory standard for blind dimensions, but industry conventions driven by window manufacturing standards create consistency. Custom blind companies can produce virtually any size, but standard sizes offer faster delivery and lower costs.
Inside Mount vs Outside Mount Sizing
Inside mount blinds install within the window frame, creating a clean integrated appearance that showcases window trim. To order inside mount blinds, measure the exact width of the window opening at the top, middle, and bottom, using the narrowest measurement. Most manufacturers automatically deduct 1/4 to 1/2 inch from your stated width to ensure the blind fits without binding. For length, measure from the top of the opening to the sill, with no deduction needed as blinds should reach the sill.
Outside mount blinds attach to the wall or window frame exterior, covering the entire opening plus surrounding area. This style blocks more light, hides unattractive frames, and works for windows without sufficient depth for inside mounting. To order outside mount blinds, measure the window width and add 3 to 6 inches total (1.5 to 3 inches per side) for light blocking and aesthetic coverage. For length, measure from desired top mounting point to desired bottom coverage, typically adding 3 to 4 inches above the frame and extending to or below the sill.
Standard Blind Widths Explained
The most common residential blind widths range from 24 to 48 inches, covering standard single and double hung windows. A 36 inch blind fits windows with 34 to 35.5 inch inside mount openings, accommodating the most popular bedroom and living room window size. Smaller widths at 18 to 23 inches suit bathroom windows, small kitchen windows, and accent openings. These narrower blinds are lighter and easier to operate, making them practical for high or hard to reach installations.
Wider blinds from 60 to 96 inches cover picture windows, patio doors, and sliding glass doors. Blinds over 60 inches wide require outside mounting in most cases because the weight and span create sagging issues with inside mounts. Very wide blinds over 96 inches may need multiple panels or specialty reinforced headrails to prevent bowing. When covering wide openings, consider splitting into two or three narrower blinds for easier operation and reduced weight on mounting hardware.
Standard Blind Lengths Explained
Blind length depends on window height and desired coverage. The most common residential lengths are 60 and 64 inches, fitting standard double hung windows in bedrooms and living rooms. Shorter lengths at 36 and 48 inches suit kitchens, bathrooms, and basement windows. These shorter blinds are less expensive and easier to clean due to reduced material. Length affects light control, with longer blinds offering more adjustability as you can lower them partially while maintaining privacy.
Floor length windows and patio doors require 72 to 96 inch lengths. Extra long blinds accumulate more weight, demanding sturdy mounting brackets and potentially motorized operation for convenience. When ordering length, consider whether you want blinds to rest on the sill, hang just above it, or extend to the floor. For inside mounts, measure to the sill. For outside mounts, add length to cover the sill and any desired additional wall space below the window.
Mounting Bracket Spacing and Installation
Mounting brackets secure the blind headrail to the window frame or wall. For blinds up to 35 inches wide, two brackets positioned 2 to 3 inches from each end provide adequate support. Wider blinds from 36 to 47 inches benefit from a third center bracket to prevent headrail sagging. Blinds over 48 inches require at least three brackets, with a fourth added for widths over 72 inches. Space brackets no more than 24 inches apart for optimal weight distribution.
Install brackets level and aligned to ensure smooth blind operation. Use a level tool and mark bracket positions with a pencil before drilling. For inside mounts, brackets attach to the top of the window frame or the frame sides, depending on blind type. Outside mounts attach to the wall above the window or to the frame face. Use appropriate anchors for your wall type: drywall anchors for drywall, toggle bolts for hollow walls, and screws directly into studs when possible for maximum strength.
Measuring Windows for Blinds
Accurate measurement is critical for proper blind fit. Use a steel tape measure, not a cloth tape, for precision. For inside mount width, measure the inside of the window frame at the top, middle, and bottom. Windows are rarely perfectly square, so use the smallest of the three measurements to ensure the blind fits at all points. Round down to the nearest 1/8 inch. For inside mount length, measure from the top of the opening to the sill at the left, center, and right, using the longest measurement to ensure full coverage.
For outside mount width, measure the window frame exterior width and add 3 to 6 inches total for overlap. This overlap blocks light gaps and creates visual balance. For outside mount length, measure from your desired top bracket position (typically 3 to 4 inches above the frame) to your desired bottom coverage point (typically at or 2 inches below the sill). Record all measurements in inches, to the nearest 1/8 inch, and double check before ordering. Mistakes in measurement are the leading cause of blind returns and delays.
Custom vs Standard Blind Sizes
Standard sized blinds are pre-manufactured in common dimensions, offering faster delivery and lower prices. Stock sizes typically include widths at 23, 27, 31, 35, 39, 47, 59, and 71 inches, with lengths at 48, 60, and 64 inches. These sizes fit the majority of standard residential windows without customization. If your window measurements fall within 1/2 inch of a standard size, you can often use the standard size with minimal gap or trimming.
Custom blinds are made to order for specific dimensions, accommodating non-standard windows, arched openings, skylights, and oversized applications. Custom orders take longer to produce, typically 7 to 14 days versus immediate availability for stock sizes, and cost 20 to 50 percent more. However, custom sizing ensures perfect fit, eliminates light gaps, and creates a polished finished appearance. For high end installations or challenging windows, custom sizing is worth the investment. Many retailers offer free measuring services to ensure accurate custom orders.
Special Considerations for Different Blind Types
Different blind styles have unique sizing considerations. Vertical blinds for patio doors typically mount outside and extend from ceiling to floor, requiring length measurements from the ceiling track to 1/2 inch above the floor to prevent dragging. Roller shades and cellular shades have minimal hardware, allowing inside mounts in shallower window frames than traditional horizontal blinds. Roman shades fold when raised, requiring additional clearance above the window for the fabric stack.
Wood and faux wood blinds are heavier than aluminum or vinyl, requiring stronger brackets and more conservative width limits. Many manufacturers limit wood blinds to 72 inches wide without center supports. Motorized blinds add weight from the motor mechanism, often requiring outside mounting for widths over 60 inches. Plantation shutters have thickness that requires 3 to 4 inches of window frame depth for inside mounting. Always check manufacturer specifications for the specific blind type you are ordering.
Practical Tips for Blind Selection and Installation
Before purchasing blinds, determine your mounting preference based on window frame depth, trim aesthetics, and light control needs. Inside mounts require at least 2 inches of frame depth for most blinds, with 3 inches preferred. Examine window frames for obstructions like locks or handles that may interfere with blind operation. Measure carefully and record all dimensions with notes about any irregularities.
When installing, gather necessary tools including a drill, level, tape measure, pencil, and appropriate screws or anchors. Follow manufacturer instructions for your specific blind type, as mounting systems vary. Test blind operation before finalizing installation to ensure smooth raising and lowering. For wide or heavy blinds, consider professional installation to ensure proper bracket placement and secure mounting. Proper sizing, careful measurement, and correct installation ensure your window blinds provide years of reliable light control, privacy, and aesthetic appeal.