Two rounding-up steps decide whether the fabric is enough
The calculator always rounds up, never to the nearest whole number, at two points: the number of fabric widths (panels) and the number of pattern repeats. Round either one down and the curtain comes up short. Example: a required width of 306 cm divided by a usable fabric width of 137 cm gives 2.23 — round up to 3 panels. Round to the nearest instead and you get 2 panels = 274 cm, 32 cm too narrow. Same logic for length: a cut length of 285 cm with a 64 cm pattern repeat gives 285 ÷ 64 = 4.45 — round up to 5 repeats = 320 cm. Round down to 4 and the result is 256 cm, shorter than the cut length needed.
Pattern repeats add more fabric than expected
A pattern repeat increases yardage well beyond a quick estimate, because every panel must be cut to the next full repeat and panels must align. Standard example: a 200 cm track, 250 cm finished length, 140 cm fabric width, 2.5x fullness, curtain tape heading. Plain fabric needs 4 panels × 285 cm = 11.4 m. With a 64 cm pattern repeat, that becomes 4 × 320 cm + 3 × 64 cm = 14.72 m — 3.32 m more. The calculator shows that addition as its own line, separate from the total.
Railroading only works on plain fabric
“Railroaded” is the English term for cutting fabric sideways, selvage running top to bottom instead of side to side. It only works when three conditions hold at once: fabric width is at least the required cut length, the pattern repeat is 0, and the pattern has no directional grain. When all three are true, seams disappear and yardage becomes the railroaded width itself rather than “cut length times panel count” — in one example that drops the requirement from 5.9 m to 3.86 m, a saving of 2.04 m. Never an option with a directional pattern or nap, such as vertical stripes or velvet.
Heading tape names and fabric width
German curtain-heading names — Kräuselband, Ösen, Schlaufen, Bleistiftfalte — appear untranslated here because they are the actual product names printed on European packaging; translating them would make the product unfindable on a shelf. Kräuselband is a universal gather tape pulled by drawstrings to form pleats; Ösen are the metal eyelet rings the rod passes through; Schlaufen are fabric tabs or loops; Bleistiftfalte is a fine “pencil” pleat. Always measure the actual fabric width before calculating — bolt widths vary by market and supplier. On a wide window, an over-width bolt (roughly 280–300 cm) removes the center seam entirely.
Fullness ratios and the US market
US decorator fabric commonly comes in 54 in (137 cm) bolts, roughly equivalent in practice to the 140 cm European standard width (⚠ this is common trade knowledge rather than something traceable to one confirmed primary source — treat it as an approximation, not a spec). Fullness is usually described as a straight multiplier — 1.5x for a minimal gather, 2x for a standard pleat, 2.5x for a fuller look, 3x for sheers needing extra body — corresponding to the same values printed as Zugverhältnis (draw ratio) on European tape packaging. Check the fabric’s actual width before calculating; mill widths vary, and using the wrong number throws off both the panel count and the pattern-repeat math above.