About the Curtain Panel Calculator
This tool applies the standard drapery math used by sewists and window-treatment retailers to turn a few measurements into a shopping list: how many fabric panels to sew, how long to cut each one, and how many yards of fabric to buy.
The formulas
- Total fabric width needed = Rod/Window Width × Fullness Ratio. A wider fullness ratio produces deeper, softer folds; a ratio near 1x hangs nearly flat.
- Panels needed = total fabric width needed ÷ fabric width per panel, rounded up to the next whole panel (a partial width still requires a full bolt-width panel).
- Cut length per panel = finished curtain length + heading/hem allowance, rounded up to the next multiple of the pattern repeat if your fabric has one.
- Total fabric to buy (yards) = (panels × cut length in inches) ÷ 36, rounded up to the nearest quarter yard since fabric is typically cut and sold in fractional-yard increments.
Choosing a fullness ratio
Fullness ratio controls how gathered the finished curtain looks. Flat panels and grommet-top styles commonly use about 1.5x the rod width; standard rod-pocket and pinch-pleat curtains use 2x to 2.5x; and lightweight sheers often use 2.5x to 3x for a soft, billowy drape. Heavier fabrics generally look better at the lower end of that range, since thick fabric bunches up faster than a lightweight one.
Heading, hem, and pattern repeat allowances
The heading and hem allowance covers the extra fabric folded over at the top (for a rod pocket or header tape) and turned under at the bottom (for a clean hem) — this defaults to 8 inches but should be adjusted for your specific style, since a simple rod-pocket header needs less than a tailored pinch pleat with a lining. If your fabric has a printed or woven pattern that must line up across panels, enter its repeat distance; the calculator rounds each panel's cut length up to the next multiple of that repeat so patterns match at the seams, which uses a bit more fabric than a plain solid.