How to Measure Windows for Mail-Order Curtains, Blinds, and Shades

Window treatments are one of the most size-sensitive home purchases you can make by mail. An inch off in either direction changes how a room looks and whether the treatment provides the light control or privacy you need. Here is the measurement process for each treatment type.

Unlike most mail-order purchases, window treatments are frequently custom or made-to-order in specific widths and lengths. That means returns, when accepted at all, often involve restocking fees, and replacements take additional lead time. Measuring correctly before ordering is not optional — it is the entire job.

Inside mount vs. outside mount: the first decision

Before you take a single measurement, decide whether your blinds or shades will mount inside the window frame (inside mount) or on the wall outside the frame (outside mount). Curtains on a rod are almost always outside mount. Hard window treatments (blinds, shades) can go either way.

Inside mount gives a cleaner look and keeps the treatment within the window frame. It requires adequate depth inside the frame for the mounting hardware — typically 1.5 to 3.5 inches depending on the product. Measure the inside frame depth before ordering an inside-mount product.

Outside mount covers more of the wall, which helps with light control and makes the window appear larger. It requires more material width and is the only option when the inside frame is too shallow or when the window has no frame depth.

Measuring for inside-mount blinds and shades

1. Width: Measure the inside width of the window frame at the top, middle, and bottom. Use the narrowest measurement. Most manufacturers will deduct a small amount (typically 0.25 to 0.5 inches) for clearance; check whether the listing says “exact deduction included” or whether you need to order your exact measurement and they handle the deduction.
2. Height: Measure from the top of the inside frame to the window sill at three points (left, center, right). Use the longest measurement to ensure the shade reaches the sill.
3. Depth: Measure the frame depth from the front of the frame to any obstacle (glass, screen, window crank). Confirm the product’s required minimum depth.

Measuring for outside-mount blinds and shades

1. Width: Measure the width of the window frame. Add 3 to 4 inches on each side (6 to 8 inches total) to overlap the frame edges for light blockage. For sheer or light-filtering treatments, 2 to 3 inches per side may be sufficient. Wider overlap provides better light control.
2. Height: Measure from where the top of the mounting bracket will sit (typically 2 to 4 inches above the frame) to where the shade will end. For a sill-length treatment, measure to the bottom of the sill. For a floor-length treatment, measure to the floor and subtract half an inch to avoid dragging.

Measuring for curtains and drape panels

Curtain measurements are rod-based, not window-frame-based.

• Rod placement (height): For standard ceilings (8 to 9 feet), mount the rod 4 to 6 inches above the window frame top, or within 2 inches of the ceiling for a taller look. Measure from the rod position to the floor for floor-length panels; subtract 0.5 to 1 inch to avoid dragging. For sill-length panels, measure from the rod to 0.5 inch below the sill.
• Rod length and panel width: The rod should extend 6 to 12 inches beyond the frame on each side so panels can stack clear of the glass when open. Panels should together equal 2 to 2.5 times the rod length for a full, gathered look. Sheer panels work at 2 to 3 times the width. Flat or minimalist panels may be 1 to 1.5 times the width.
• Panel length: Curtain panels are sold in standard lengths: 63, 84, 95, 108, and 120 inches are the most common. Match your floor-to-rod measurement to the appropriate panel length.

Common mistakes to avoid

• Measuring only once. Windows are rarely perfectly square. Always measure in three positions for both width and height.
• Forgetting to specify inside or outside mount when ordering. These require different widths and result in very different looks.
• Ordering the frame width for curtains rather than the full rod extent. Curtains should cover the frame and the wall beyond it when drawn.
• Using a cloth tape measure instead of a rigid steel tape. Cloth tapes stretch and produce inaccurate measurements at longer lengths.

Custom window treatments ordered in the wrong size are one of the most expensive and least returnable mistakes in home furnishing. Five minutes with a steel tape measure and this checklist prevents the problem entirely.