How to Calculate Curtain Fabric: Fullness, Hems and Pattern Repeats
Calculate curtain fabric for two panels using track width, fullness, hems and pattern repeat. Separate finished dimensions from the fabric you must buy.
A useful starting point
Choose the heading and fullness first, then calculate whole fabric widths for each of two equal panels. Add top and bottom allowances to the finished drop, account for straight repeat and confirm the final cutting plan with the workroom.
Curtain fabric quantity is not simply window width times window height. Fullness, side hems, heading allowances and the number of full fabric widths all matter.
The BIID window-survey guide treats survey information and the intended curtain design together. The arithmetic below is our own simplified two-panel example, not a reproduction of its workroom templates.
Measure the track and finished drop
Use the planned pole or track width, not automatically the glass width. Define exactly where the finished drop starts and ends for the selected heading.
Record fabric width, the maker's required fullness, side-hem allowance per edge, top allowance and bottom hem. Keep widths and drops distinct when reading the unit conversion reference.
Calculate two equal panels
Assume a 2 m track, chosen fullness of 2, 1.4 m-wide fabric and 0.05 m side hems on each edge. Our example's finished drop is 2.4 m, top allowance 0.15 m and bottom hem 0.2 m.
| Step | Result |
|---|---|
| Flat finished width per panel | 2 × 2 ÷ 2 = 2 m |
| Width including two side hems | 2 + 0.10 = 2.1 m |
| Whole fabric widths per panel | round up 2.1 ÷ 1.4 = 2 |
| Fabric widths for both panels | 4 |
| Unmatched cutting drop | 2.4 + 0.15 + 0.2 = 2.75 m |
| Unmatched fabric length | 4 × 2.75 = 11 m |
Use the curtain fabric calculator to repeat the calculation with your actual fabric and heading choices. Fullness of 2 is an example input, not a universal recommendation.
Add a straight pattern repeat
If the full vertical repeat is 0.3 m, round the 2.75 m cut upward to ten repeats: 3 m. Four widths then need 12 m before any workroom-specific positioning allowance.
This John Lewis curtain-fabric specification lists fabric width, vertical repeat and match type as distinct fields. Read those fields for your selected fabric. Do not assume a half-drop, directional or placement fabric follows a straight-repeat estimate.
Agree the cutting plan before buying
This calculator models two equal panels and rounds fabric widths separately for each. It does not estimate lining, interlining, blinds, fabric shrinkage or a half-drop cutting sequence.
If the fabric can be used sideways, establish that orientation and its suitability with the workroom before entering dimensions. Do not swap roll width and finished drop just to reduce the order.
Common questions
Can I measure only the window opening?
That may miss the track extensions and the intended floor or sill relationship. Measure the actual proposed hanging arrangement.
Are seams and hems already included?
Only the allowances you entered are included. Confirm seam practice and any extra repeat needed to position the motif. Keep sewing, lining and installation as separate lines in the renovation budget; coordinate the result with your room's wallpaper plan.
