How the calculation works
The formulas
Finished flat panel width means fabric width before gathering. Each panel receives whole fabric widths; cutting drop adds heading and bottom hem, then rounds up for a vertical repeat if entered.
Flat panel width = track width × fullness ÷ 2
Widths per panel = ceil((flat panel width + 2 × side hem) ÷ usable fabric width)
Cut drop = finished drop + heading + bottom hem (round up to repeat)
Fabric length = 2 × widths per panel × cut drop
Assumptions to check
- Two equal panels and vertical joins are assumed; entered fabric width must be usable after selvedges.
- Side hem is per side of each finished panel. Lining, interlining, and horizontal motif alignment are not included.
A worked example
A 3 m track at 2× fullness gives two 3 m flat panels. With 1.4 m usable fabric and 5 cm side hems, each uses 3 widths. At a 2.7 m cutting drop, total fabric is 16.2 m.