Last updated: 2026-06-19

Curtain Fabric

Curtain fabric yardage is the total length of fabric needed to sew curtain panels, set by how wide the gathered fabric must be across the window and how long each piece must be cut to cover the drop and hems. This calculator estimates the number of fabric widths to join and the total fabric to buy, including an allowance for any vertical pattern repeat.

Widths across the window

Curtains hang in folds, so the flat fabric is far wider than the window. The fullness ratio sets how much wider: multiplying the window width by the fullness gives the gathered width, and dividing by the width of the fabric bolt gives the number of widths to join side by side. Because partial widths cannot be used, the result is rounded up:

where $W$ is the window width, $f$ is the fullness ratio, and $b$ is the fabric width. A fullness of about 2.0 suits standard pleated headings.

Cut length down the drop

Each width is cut to the finished drop plus the header and bottom hems. When the fabric carries a vertical pattern repeat $r$, every cut is rounded up to a whole number of repeats so the pattern aligns across the joined widths:

For plain fabric with no pattern repeat, the cut length is simply the drop plus hems, $D + h$. The total fabric is the number of widths times the cut length, $T = n \cdot L$.

Worked example

The pattern repeat is the input most often overlooked, since it adds waste at the top of every width. Confirm the heading type and seam allowances before cutting, and buy from a single dye lot so the colour stays consistent.

To plan the proportions of the finished panels, see Aspect Ratio Calculator.