How to calculate curtain fabric: fullness, widths, pattern repeat and railroading

Six inputs are required: track length, returns and overlaps, finished drop, heading type (which sets fullness), fabric width and pattern repeat. Missing any of them makes the quantity unreliable.

• Track length: measured using the on-site curtain survey method, not taken from the window opening.
• Returns and overlaps: the fabric that wraps back to the wall or pocket at each end, and the overlap where a pair meets.
• Finished drop: from the suspension point to the hem, based on finished floor level.
• Heading type: pinch pleat, wave, eyelet and others set the fullness; see curtain heading types.
• Fabric width: standard widths are around 140–150 cm; wide widths around 280–300 cm.
• Pattern repeat and match type: shown on the fabric label or sample card.

Fullness is the ratio of flat fabric width to the curtain's closed width. Pleated curtains typically use 2–2.5 times; eyelet and wave curtains are similar or lower depending on the system.

Cutting fullness to save fabric makes curtains look flat and sparse, which is especially visible on sheers. State the fullness on the specification so the workroom and the cost estimate use the same figure. When creating a project on SEAMATER, entering fullness and heading type per window keeps the quotation aligned with the real quantity.

The calculation runs in four steps: flat width, number of widths, cut drop and total metres. Allowances below are typical; every workroom has its own, so confirm them before fixing the BOQ.

For a 3 m track with 2.5x pinch pleat in a 140 cm patterned fabric with a 64 cm repeat, about 23.1 m is needed. The same curtain in a plain fabric needs about 19.3 m.

Inputs

• Track 300 cm, centre-opening pair.
• Returns 8 cm each end; overlap 5 cm per panel.
• Finished drop 250 cm.
• Fullness 2.5; hem 15 cm; heading 10 cm; side hems 5 cm per edge.
• Fabric 140 cm wide, 137 cm usable, 64 cm vertical repeat, straight match.

Steps

1. Width to cover: 300 + 2 × 8 + 2 × 5 = 326 cm.
2. Apply fullness: 326 × 2.5 = 815 cm.
3. Add side hems for 4 edges (2 panels): 815 + 4 × 5 = 835 cm.
4. Widths: 835 ÷ 137 = 6.09, rounded up to 7 widths, or 3.5 per panel.
5. Plain cut drop: 250 + 15 + 10 = 275 cm.
6. Round to repeat: 275 ÷ 64 = 4.30, rounded up to 5 repeats, so 5 × 64 = 320 cm per width.
7. Total: 7 × 320 = 2,240 cm, plus one 64 cm repeat to position the first cut, gives 2,304 cm, or 23.04 m. Order about 23.1 m.

In a plain fabric: 7 × 275 = 1,925 cm, or 19.25 m; order about 19.3 m. The pattern adds 3.79 m, roughly 20%. Accepting 6 widths would reduce actual fullness to about 2.46 (6 × 137 − 20 = 802 cm, divided by 326 cm), an option only if the design team agrees.

Wide-width fabrics of 280–300 cm are usually railroaded: the fabric width becomes the curtain height, so there are no vertical seams and the metres needed are close to the flat width. The cut drop must be less than the usable fabric width.

Example: wave sheer on 280 cm fabric

1. Width to cover is again 326 cm (300 cm track, same returns and overlaps).
2. Fullness 2.0: 326 × 2 = 652 cm; plus side hems 4 × 5 = 20 cm gives 672 cm.
3. Check height: 250 + 10 hem + 8 heading = 268 cm, which is less than the usable width of about 276 cm (280 cm less 2 cm selvedge each side).
4. Metres: 672 cm plus 5 cm cutting allowance per panel (2 panels) gives 682 cm, or 6.82 m. Order about 6.9 m.

For comparison, a 140 cm sheer used vertically needs 672 ÷ 137 = 4.91, rounded up to 5 widths × 268 cm = 1,340 cm, or 13.4 m, plus four visible vertical seams. Railroading only works when the design and weave direction allow the fabric to be turned; check with the manufacturer for pile fabrics or one-way patterns.

The larger the repeat, the more fabric is wasted per width, because each cut drop rounds up to a whole number of repeats. Half-drop matches usually need more fabric than straight matches.

• Straight match: the pattern sits at the same height on both edges; every width starts at the same point.
• Half-drop match: the pattern on the next width is offset by half a repeat; many workrooms add half a repeat per cut or plan alternating cuts.
• Horizontal repeat: affects seam positions and how the motif is centred on each panel.

For large motifs, fix where the pattern starts at the heading or hem on the drawing, because that decision changes cutting and quantity.

Lining uses the same number of widths as the face fabric, needs no pattern rounding and is cut slightly shorter, because it usually finishes about 2.5 cm above the curtain hem.

For the pinch pleat example above, a 140 cm lining also needs 7 widths. With a cut drop of about 270 cm (around 5 cm shorter than the face fabric because of the raised lining hem and heading), the total is 7 × 270 = 1,890 cm, or 18.9 m. For blackout linings, order the full project quantity at the outset so the window-facing colour is consistent from outside.

Record quantities per window ID, separating face fabric, lining and hardware, with the assumptions used. This lets QS teams and suppliers cross-check quickly.

1. List window ID, track length, finished drop and heading type.
2. State fullness, fabric width, repeat and number of widths.
3. Give face and lining metres per window, then total by fabric code.
4. Order each fabric code's full quantity at the outset, since top-up orders may differ in colour between production runs.
5. Add fabric for a mock-up room where the project requires one.

See writing BOQ lines for curtains, wallcoverings and rugs and the curtain terminology glossary so all parties use the same terms. On SEAMATER, home fabrics are sold by the metre and fabric quantity is checked for the customer: send window sizes, heading types and fabric codes, and the widths and metres are cross-checked. The method is the same for projects in Vietnam and overseas.