Curtain Size Calculator
Work out curtain rod width, finished panel length and how many ready-made panels you need for a properly full, correctly hung window treatment.
How it works
Rod width = window width + 2 × extension · Fabric width = rod width × fullness · Panels = fabric width ÷ 50 (rounded up) · Panel length = rod height ± hem offset
Curtains should extend well past the glass so drawn panels stack on the wall, not the window, which is why the rod runs several inches beyond each side. To look full rather than flat, the flat fabric across the window needs to be about twice the rod width; that total is then divided by the width of a ready-made panel (about 50 inches) to count panels. Length is measured from the rod to the desired hem, adjusting for whether you want the panels to float just above the floor, kiss it, or puddle.
Worked example
A 36-inch window with 8-inch extensions gives a 36 + 16 = 52-inch rod. At 2× fullness you need 104 inches of fabric — three 50-inch panels. Hung at 84 inches in a float style, each panel is hemmed to 84 − 0.5 ≈ 83–84 inches.
Frequently asked questions
How wide should curtains be compared to the window?
The flat width of all panels combined should be about 2 to 2.5 times the rod width so the fabric gathers into folds. At 1× the panels would pull flat and stretched when closed.
How high should I mount the curtain rod?
Mount the rod several inches above the window frame — often halfway between the frame and the ceiling — to make the window and room feel taller. This calculator measures panel length from that rod height down to the floor.
What is the difference between float, kiss and puddle hems?
A float hem stops about half an inch above the floor (easiest to vacuum around), a kiss hem just touches it, and a puddle hem adds several inches of fabric that pools on the floor for a formal look.
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This calculator is for educational purposes. Double-check important results before acting on them.