Curtain Size Calculator

How to Measure for Curtains

Getting curtain measurements right comes down to four numbers: window width, rod extension, rod height, and the drop style you want. The window width is measured inside trim to inside trim. The rod extension is how far the rod reaches past each side of the window, which controls how much the open curtains stack off the glass. Rod height is measured from where the rod will actually sit, not the top of the window, down to the floor. Drop style then adds or subtracts a small amount to create the look you want at the floor.

Once you have the rod width (window width plus both side extensions), you multiply by the fullness factor to get total fabric width needed. Divide that by the number of panels to get the per-panel width. For ready-made curtains, divide total fabric width by the standard panel width (usually 50 to 54 inches) and round up to whole panels.

Rod Height and Where to Mount

Mounting the rod 4 to 6 inches above the window frame is a common starting point for most rooms. For rooms with high ceilings or where you want a more dramatic look, mounting the rod 8 to 12 inches above the window, or even close to the ceiling, makes the space feel taller and more formal. The key measurement for the calculator is not the window height but the distance from the rod location to the floor, since that is what determines panel length.

Fullness by Style

Fullness is the ratio of total fabric width to the rod width. A fullness of 2x means you're using twice as much fabric as the rod is wide, which creates a well-gathered appearance. For grommet and rod-pocket panels, 1.5x to 2x is the standard range and gives a clean, contemporary look. Pleated styles need 2x to 2.5x to pleat properly. Sheer fabrics look best at 2x or more because they're lighter and need extra volume to look full rather than sparse when closed.

Drop Styles Explained

Standard US Curtain Sizes

Ready-made curtain panels in the US come in standard lengths of 63, 84, 95/96, 108, and 120 inches. Panel widths are typically 50 to 54 inches each. If your calculated length falls between standard sizes, round up and hem the panels to the correct length. Custom panels are worth considering when standard sizes don't work, particularly for very wide windows or unusually high ceilings.

Tips for a Professional Result

Mount the rod higher and extend it wider than you think you need. Rods that sit close to the ceiling and extend well past the window frame make rooms feel larger and windows feel more architectural. For the fullest look with closed panels, lean toward 2x fullness or higher. For an airy, modern look with panels mostly open, 1.5x is sufficient. Always order at least one extra panel if you're uncertain about the fullness calculation.

Frequently Asked Questions

Curtain Planning Checklist

Before ordering, confirm rod bracket placement, wall anchor type for your wall material, and whether your chosen panels are machine washable or dry-clean only.

Planning use only. See Methodology and Data Sources. View all project checklists →

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