Scale to GramsHow to Measure a Window for Blinds and Curtains
Inside Mount vs. Outside Mount
Before measuring anything, decide whether you want an inside mount (blinds fit inside the window frame) or outside mount (blinds attach to the wall above and around the frame). Inside mount creates a clean, built-in look and does not cover any wall space, but requires a window frame depth of at least 1-2 inches. Outside mount covers the entire window opening and can make windows appear larger, and works on any window regardless of frame depth. The measurements you need are completely different for each type, so this decision must come first. Most modern homes use inside mount for a streamlined look, but outside mount is better for blocking more light and covering imperfect or narrow window frames.
Inside Mount Measurements
For inside mount, you need the exact inside dimensions of the window opening. Measure the width at three points: top, middle, and bottom. Use the narrowest measurement — blinds that are too wide will not fit into the frame. Measure the height at three points: left, center, and right. Use the longest measurement to ensure full coverage. Record all measurements to the nearest eighth of an inch. Do not make any deductions — most blind manufacturers will subtract the necessary clearance (typically 1/4 to 1/2 inch) from your width measurement. If you deduct clearance yourself and the manufacturer also deducts, your blinds will be too narrow and have visible light gaps. Also measure the frame depth from the front edge to the glass — most inside-mount blinds need at least 1.5 inches of depth, and some styles (cellular shades, wood blinds) need up to 3 inches.
Outside Mount Measurements
For outside mount, measure the total area you want to cover. Width should extend at least 1.5 inches beyond the window opening on each side (3 inches total added to the opening width) to minimize light leakage. More overlap (2-3 inches per side) provides better light blocking. Height should extend at least 1.5 inches above the window opening to allow room for the mounting hardware, and at least 0.5 inches below the opening (or to the window sill). For curtains, extend the rod 3-6 inches beyond each side of the window and mount it 4-6 inches above the frame for a full, luxurious look that makes the window appear taller and wider.
Common Measurement Mistakes
The most common error is measuring only once at one point. Windows are rarely perfectly square — even in new construction, the width at the top can differ from the width at the bottom by a quarter inch or more. Measuring at three points catches this variation. The second most common mistake is rounding measurements. Blinds are manufactured to precise specifications, and rounding 36 3/8 inches to 36.5 inches creates a blind that is 1/8 inch too wide for inside mount — which means it will not fit. Always measure to the nearest 1/8 inch. The third mistake is confusing inside and outside mount instructions on the order form. Double-check which type you selected before submitting dimensions.
Using AI Photo Measurement
If you need a quick estimate before committing to precise measurements, AI photo tools can help. Photograph the window with a reference object of known size in the frame — a ruler, a credit card taped to the frame, or even a standard light switch plate (which is 2.75 inches wide). The AI estimates the window dimensions from the photo, which is useful for getting a ballpark figure when shopping or when measuring a window in a property you do not yet own. For final ordering, always follow up with physical tape-measure measurements. Use Scale to Grams' measurement tools to photograph your windows and get instant dimension estimates for initial planning.
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