Curtain Size Calculator

Curtain fabric estimation requires measuring window width and desired drop length, then accounting for fullness ratio (how gathered the curtain is), hem allowances, and header allowances. Getting this right ensures curtains look full and luxurious rather than flat and underfed.

Fabric Width Required formula: Total Fabric Width = Window Width × Fullness Ratio × Number of Panels

Fabric Length Required per Panel: Cut Length = Finished Drop + Top Hem Allowance + Bottom Hem Allowance + Pattern Repeat

What each variable means:

• Window Width: measure the pole or track width, not just the window opening; for a full look, the pole should extend 15–30 cm beyond each side of the window
• Fullness Ratio: how much fabric width relative to the pole width; standard is 2.0× to 2.5× for a full look; sheer panels may use 3× for a floaty effect; tab-top panels can get away with 1.5×
• Finished Drop: from the pole to where the curtain should end, which is not the same as the window height. Measure from the pole, not the top of the glass. 1–2 cm above the floor for a modern look; touching the floor for an elegant look; 15–25 cm puddled on the floor for a dramatic romantic style
• Header Allowance: the fabric turned over at the top, which depends entirely on the header. A rod pocket or pinch pleat needs 12 cm (5 in); an eyelet or grommet header needs only 4 cm (1.5 in) because the ring reinforces the edge; a tab top sits in between at about 5 cm (2 in)
• Bottom Hem: 15 cm (6 in) doubled over gives the weight that makes a curtain hang straight instead of kicking out at the floor
• Pattern Repeat: vertical distance of any fabric pattern; each panel must start at the same point in the repeat, so you add one full repeat per panel as matching allowance

Worked example: Pole 180 cm wide. Finished drop 250 cm, floor length. Two panels, 2.5× fullness, pinch pleat header, pattern repeat 30 cm.

Total fabric width = 180 × 2.5 = 450 cm; two panels → each panel 225 cm wide Cut length = 250 + 12 (header) + 15 (bottom hem) + 30 (pattern) = 307 cm per panel

Total fabric ordered = 2 panels × 225 cm wide, so buy 225 cm width or wider fabric. Yardage = 2 panels × 307 cm = 614 cm = 6.14 meters (order 6.5 m to have margin)

Lining note: Interlining or blackout lining is cut the same width but 10 cm shorter than the face fabric (no pattern matching needed for lining).