Blind Size Calculator

Windows are rarely perfectly square, which is why precise measurement requires checking multiple points across the frame. The calculator evaluates three width points (top, middle, and bottom) and three height points (left, center, and right) to identify structural inconsistencies. For an inside mount, it automatically selects the minimum width to ensure the blind fits inside the recess, and the minimum height to prevent clearance issues. Depending on whether you are planning an inside or outside mount, standard fabrication formulas add clearance margins (such as plus 3 inches for width and plus 1.5 inches for height) to block light effectively, or make slight deductions for proper operating clearance.

Imagine you are measuring a standard living room window for inside-mount horizontal blinds. You take three width measurements: widthTop at 35.2 inches, widthMiddle at 35.0 inches, and widthBottom at 35.1 inches. Next, you measure the height at three points: heightLeft at 48.0 inches, heightCenter at 48.2 inches, and heightRight at 48.1 inches. The calculator first finds the minimum width (35.0 inches) and minimum height (48.0 inches). For an inside mount, the finished blind width uses the minimum width (35.0 inches) minus a tiny manufacturing tolerance, while a customized outside mount would add extra inches to overlap the trim completely.

Always use a reliable steel tape measure rather than a cloth tailor's tape, which can stretch or bend over window sills. Always measure to the nearest 1/8 of an inch, as rounding up or down too aggressively can leave your blinds unable to fit or properly latch. Finally, clearly distinguish between inside mount (measuring inside the window casing) and outside mount (measuring the outer frame or trim), because mixing up these two installation styles will result in incorrect dimensions.