Window Blinds Calculator — Measure for Perfect Fit
Order Blind Width
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Order Blind Height
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Notes
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How to Measure Windows for Blinds
Accurate window measurements are the single most important step when ordering blinds, since even a quarter-inch error can result in gaps, binding, or a poor fit. There are two mounting options: inside mount, where the blind sits within the window frame for a clean built-in look, and outside mount, where the blind covers the entire frame and extends beyond it. Inside mount requires at least 1.5 inches of window depth for most blind types, and deeper windows of 3 inches or more allow the blind to sit fully recessed.
For inside mount, this calculator deducts a standard 1/4 inch from your measured width to provide operating clearance so the blind can raise and lower without scraping the frame. You should measure width at three points -- top, middle, and bottom -- and use the narrowest measurement, since window frames are rarely perfectly square. For height, measure at left, center, and right, and use the longest measurement. Outside mount adds 1.5 inches on each side and 3 inches to the height for full light-blocking overlap.
Common blind sizes use half-inch increments, and most manufacturers can custom-cut to your exact dimensions. When ordering, always measure to the nearest 1/8 inch using a steel tape measure rather than a fabric one. If you are covering multiple windows in the same room, measure each window individually rather than assuming they are all the same size. Even windows that appear identical often differ by 1/4 to 1/2 inch due to settling and construction tolerances.
Frequently Asked Questions
Inside mount vs outside mount?
Inside mount looks cleaner and takes less material but requires at least 1.5" of window depth. Outside mount covers the entire window frame, provides better light blocking, and makes windows appear larger.
How do I measure for blinds?
For inside mount, measure width at top, middle, and bottom — use the smallest measurement. For height, measure left, center, and right — use the longest. Measure to the nearest 1/8 inch.
Should I deduct for inside mount?
Most blind manufacturers build in a small deduction. Check with your specific manufacturer. Generally, deduct 1/4 to 1/2 inch from width for inside mount clearance.