# Curtain fabric calculator

To find how much curtain fabric you need, multiply the track width by the fullness to get the flat width each curtain must cover, divide that by the usable width of your fabric to get a whole number of fabric widths, then multiply that count by the cut length — the finished drop plus a heading allowance plus a hem allowance, rounded up to a whole number of pattern repeats. The calculator below does this for metric or imperial measurements and shows every step, so you can adjust any allowance to match how your curtains are being made.

Source: https://fabricmeasure.com/calculators/curtain-fabric-calculator/
Last updated: 2026-08-20 (method v1)
Published by FabricMeasure.

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## The formula

Two independent quantities, multiplied at the end.

**Across — how many fabric widths each curtain needs:**

```
requiredFlatWidth = (trackWidth + returns + overlap) x fullness / panels
usable(W)         = W x fabricWidth - 2 x sideHem - (W - 1) x 2 x seamAllowance
widthsPerPanel    = smallest whole W where usable(W) >= requiredFlatWidth
```

Side hems apply to the two OUTER edges only; interior edges are seams.

**Down — how long each cut must be:**

```
rawCutLength = finishedDrop + headerAllowance + hemAllowance
cutLength    = patternRepeat > 0
                 ? ceil(rawCutLength / patternRepeat) x patternRepeat
                 : rawCutLength
totalCuts    = widthsPerPanel x panels
totalLength  = totalCuts x cutLength
                 + patternRepeat        (one repeat, for pattern placement)
                 + shrinkage
```

Every rounding step rounds UP, never to nearest.

## Default allowances (all editable on the page)

| Heading | Heading allowance | Hem | Minimum fullness |
| --- | --- | --- | --- |
| Pencil pleat | 15 cm | 20 cm | 2x |
| Pinch pleat | 20 cm | 20 cm | 2x |
| Eyelet | 25 cm | 20 cm | 1.8x |
| Tab top | 12 cm | 20 cm | 1.5x |
| Wave | 15 cm | 20 cm | 2x |

Side hem 8 cm per side. Seam allowance 1.5 cm. Lining 137 cm wide, cut 2.5 cm shorter than the face fabric.

## Worked example

200 cm track, 220 cm drop, a pair of pencil-pleat curtains, 140 cm fabric, 2x fullness, 32 cm pattern repeat.

| Step | Working | Result |
| --- | --- | --- |
| Flat fabric width needed, per curtain | (200 cm track + 0 cm returns + 0 cm overlap) × 2 fullness ÷ 2 curtains | 200 cm |
| Fabric widths per curtain | 2 × 140 cm − 16 cm side hems − 3 cm seams = 261 cm usable | 2 widths |
| Fullness you actually get | 2 × 261 cm ÷ 200 cm of track | 2.61× |
| Cut length before pattern matching | 220 cm drop + 15 cm heading + 20 cm hem | 255 cm |
| Cut length rounded to whole pattern repeats | ⌈255 cm ÷ 32 cm⌉ = 8 repeats × 32 cm | 256 cm |
| Total cuts to buy | 2 widths × 2 curtains | 4 cuts |
| Fabric for the cuts | 4 × 256 cm | 1024 cm |
| Pattern placement allowance | one extra repeat, so the first cut can start where you want in the pattern | 32 cm |
| Total fabric required | cuts + placement + shrinkage | 1056 cm |
| Buy, rounded up (nearest 10 cm) | 1056 cm rounded up to the next 0.1 m | 1060 cm |

## Assumptions

- The drop is measured from the hook, ring or eyelet position, not the top of the pole.
- The pattern repeat is a straight repeat; half-drop repeats need an extra half repeat per additional width and are not modelled.
- The fabric width is nominal and includes the selvedge; enter the usable width if known.
- The fabric runs vertically. Railroading is not modelled.
- Lining is calculated separately and is not included in the face-fabric figure.

## Common questions

### Do I measure the window or the curtain track?

Measure the track or pole, not the window. A track normally extends 15–20 cm past the window on each side so the curtains can stack clear of the glass, and measuring the window instead is the most common reason a calculation comes out short.

### Why does the calculator give more fullness than I asked for?

Because fabric is sold in whole widths. If two curtains need 200 cm of flat fabric each and one width gives 124 cm, you have to buy two widths — 261 cm — and the extra becomes fullness. The result shows both the fullness you asked for and the fullness you will actually get.

### How does a pattern repeat change how much I need?

Every drop has to start at the same point in the pattern or the motifs will not line up across the joins, so each cut length is rounded up to a whole number of repeats. A 255 cm cut against a 32 cm repeat becomes 256 cm. One extra repeat is also added so the first cut can be placed where you want it in the design.

### Where do I measure the drop from?

From the hook, ring or eyelet position down to where you want the hem to finish — not from the top of the pole. The difference is usually 2–4 cm, which is enough to matter on a floor-length curtain.

### Does this include lining?

The main figure is face fabric only. Lining is a separate purchase calculated from a narrower roll with no pattern to match, and is shown as its own result underneath.

## Related tools

- [Curtain fullness calculator](https://fabricmeasure.com/calculators/curtain-fullness-calculator/): How many widths each curtain needs at the fullness you want — and what whole widths really gather to.
- [Roman blind fabric calculator](https://fabricmeasure.com/calculators/roman-blind-fabric-calculator/): Fabric and lining for a flat blind — no fullness, but the repeat still decides the cut.
- [Curtain lining calculator](https://fabricmeasure.com/calculators/curtain-lining-calculator/): Lining on its own narrower roll, from the flat width your curtains already need.
- [Curtain heading types](https://fabricmeasure.com/charts/curtain-heading-types/): Five headings compared on fullness, allowance and what they cost in cloth.
- [Standard curtain sizes](https://fabricmeasure.com/charts/standard-curtain-sizes/): Ready-made drops and widths, in both systems — and what each width really gathers to.
- [Pattern repeat calculator](https://fabricmeasure.com/calculators/pattern-repeat-calculator/): The cut length a repeat forces, what is trimmed from every piece, and what matching the design costs.