How do I measure windows for blinds?

Choose inside or outside mount first, then measure with a steel tape in three places, write down the narrowest width and the longest height for an inside mount, and do not subtract anything yourself. The maker adjusts for clearance. Most mistakes come from guessing at that step.

The guidance here follows a window-covering manufacturer's published measuring guide for its natural shades; always check the maker's instructions for the specific blind you order.^[1]

Choose inside or outside mount

An inside mount sits within the window casing, which shows off the trim and gives a clean look. An outside mount goes on the wall or molding around the window. Outside mounts are ideal for covering windows that are not square, and they cut light gaps at the sides.^[1]

Inside mounts have limits. A blind made to fit inside the casing leaves a small gap on each side, and the stack of the raised blind blocks part of the view.^[1] Window handles and cranks can also get in the way. Outside mount brackets need at least 2 inches of flat surface above the window or on the window frame.^[1]

Tools

Use a steel tape measure, not a cloth one, and round measurements to the nearest 1/8 inch.^[1] Keep a pencil and a simple worksheet handy. Bali tells buyers to measure each window and record its location, because size variances are common.^[1] Two windows side by side can differ.

Inside mount: step by step

Check the depth of the casing first. Each blind has a minimum depth for the headrail, and the figure varies by product, so find it in the maker's chart before you measure anything else.^[1]

Measure the inside width of the casing in three places and record the narrowest measurement.^[1] Then measure the inside height from the top of the casing to the top of the sill in three places and record the longest measurement.^[1]

Do not take any deductions for clearance, because the manufacturer will take 1/2 inch off the overall width for a perfect fit.^[1] If you subtract as well, the blind will be too small and leave visible gaps.

Outside mount: step by step

For width, measure the area you want to cover. Bali recommends 1½ inches of overlap on each side of the window, 3 inches in total, for optimum light control and privacy.^[1] Decide where the headrail will go, on the molding or above it, and mark the spot. Measure height from that mark down to the sill, or lower if you want more overlap.^[1]

For outside mounts, the manufacturer makes no deductions, so order the exact measurement you recorded.^[1]

Record and double-check

Write the width first and the height second for every window, label the room and window, and measure again before ordering. A custom blind is cut to your numbers, so ask the seller about its remake policy before you order.

Ordering for a home with children

Corded blinds are a strangulation hazard for young children.^[2] Custom window coverings must now meet the same operating-cord requirements as stock products,^[2] because accessible cords can strangle young children. When you order, ask for a cordless or otherwise inaccessible-cord design, especially for bedrooms and play areas.

Stop and call a pro if

• The window is arched, angled, curved or oversized. Shapes like these are easy to mismeasure and costly to recut; ask the supplier for a measure-and-quote visit.
• The casing is out of square by a lot. If the three width readings differ noticeably, an outside mount or a professional measure is the safer route.
• Mounting would mean cutting into framing, drilling into masonry or reaching a high window from a tall ladder. Hand that part to an installer.
• You are ordering motorized blinds. Power wiring is for a licensed electrician.

Getting help in Virginia

Once you have your numbers, read how much custom blinds cost in Virginia and whether custom window treatments are worth it before you order. Browse more interiors answers or see interiors services near you.

If you would rather have someone measure and install, describe your windows and local businesses can send written quotes.