Accurate measurements are the single most important factor in getting custom blinds that fit perfectly. A measurement error of even 1/4 inch can result in light gaps, a blind that does not fit the frame, or one that rubs against the sides. This guide covers everything you need to know about measuring for both inside mount and outside mount installations.

Tools You Will Need

Use a steel tape measure (not a cloth tape) for accuracy. Have a notepad and pencil ready to record measurements immediately. A step stool may be needed for high windows. Measure in inches to the nearest 1/8 inch.

Inside Mount Measurements

Inside mount blinds fit within the window frame for a clean, built-in look. This is the most popular mounting style for modern homes.

Width: Measure the inside width of the window frame at three points — top, middle, and bottom. Record the narrowest measurement. This ensures the blind will fit at the tightest point.

Height: Measure the inside height at three points — left, centre, and right. Record the longest measurement. This ensures full coverage at the tallest point.

Depth: Measure the depth of the window frame to ensure the blind will fit without protruding. Most blinds require at least 2 inches of depth for inside mount. Check our detailed measurement guide for specific depth requirements by product type.

Outside Mount Measurements

Outside mount blinds are installed on the wall or frame above the window, covering the entire opening plus overlap. Choose outside mount when your window frame is too shallow for inside mount, when you want to make windows appear larger, or when you need maximum light blocking.

Width: Measure the area you want to cover. Add at least 2-3 inches on each side beyond the window opening for proper light blocking and a finished look.

Height: Measure from where you want the top of the blind (typically 3-4 inches above the window frame) to where you want the bottom (typically at or below the window sill).

Common Mistakes to Avoid

Do not assume all windows are the same size — measure each one individually.

Do not round measurements up or down — record the exact measurement to 1/8 inch.

Do not measure from the outside of the frame for inside mount — measure the inside opening only.

Do not forget to check for obstructions (handles, locks, trim) that might interfere with the blind operation.

For detailed diagrams and step-by-step instructions, visit our complete measurement guide. Ready to order? Configure your custom blinds with instant pricing.