Curtain Fabric Calculator

Curtains are not measured, they are calculated, and the calculation has three traps. The width you buy is the track times a fullness ratio, because a curtain that does not gather hangs like a bedsheet. The length you buy is the drop plus a deep hem and a heading allowance. And a patterned fabric has to start at the same point on every width, so each cut is rounded up to a whole repeat.

Track or pole width, in centimetres

The track itself, not the window.

Finished drop, in centimetres

From the hooks to where you want the hem.

Heading

Fabric width, in centimetres

Off the roll; 137 is common for furnishing fabric.

Pattern repeat, in centimetres

0 for a plain fabric.

Hem, in centimetres

Doubled in the cut length. Fifteen is a good deep hem.

Stack-back either side, in centimetres

Extra track for the curtain to gather onto when open.

A pair, meeting in the middle

17.28m

6 widths cut at 288cm — 3 in each curtain. The finished curtain gathers 3.26 times the 230cm it covers.

✓ The curtain gathers to at least the fullness for that heading — 3.26 times the 230cm it covers, against the 2.5 a pencil pleat wants
✓ Each cut length holds the drop, the hem and the heading — 288cm cut for a 220cm drop, with 15cm of hem doubled and the heading allowance
✓ Every cut is a whole number of pattern repeats — 9 repeats of 32cm, wasting 30cm on each cut
✓ The metres are the widths times the cut length — 6 widths at 288cm makes 17.28m
✓ A pair gets an even number of widths — 3 widths in each curtain, so the two match

What this generator does

Multiplies the track by the heading's fullness, divides by the usable fabric width to get the number of widths, and works the cut length out from the drop, the hems and the pattern repeat.

How to use this tool

Measure the track — not the window — and the drop from the hooks.
Choose the heading, which sets how full the curtain has to be.
Type the fabric width and pattern repeat off the roll.
Read the metres, and how they are cut into widths.

Understanding the controls

Track or pole width: The track itself, in centimetres — not the window, which is usually narrower. The curtains have to cover the track.
Finished drop: From the hooks down to where the hem should sit. The cut length is longer than this, which is the point of the calculation.
Heading: What gathers the top: a pencil pleat wants two and a half times the width, a pinch pleat or wave a little over two, an eyelet twice, a tab top less. Each also needs a different allowance at the top.
Fabric width: Off the roll. Furnishing fabric is often 137cm; dress fabric is narrower and takes more widths.
Pattern repeat: How far apart the design repeats. Every width is cut to a whole number of these so the pattern matches across the seams. Zero for a plain fabric.
Hem: The bottom hem, which is doubled over in the cut length. Fifteen centimetres gives a good weighty hem.
Stack-back either side: The extra width beyond the window that the curtain gathers onto when open, so it does not block the light.
A pair, meeting in the middle: A pair needs an even number of widths so both curtains are the same. A single curtain can take an odd number.

Common use cases

Buying fabric for curtains you are having made
Checking a quote before agreeing to it
Seeing what a large pattern repeat adds to the bill
Comparing a pencil pleat against an eyelet heading on cost
Working out whether a remnant is enough for one curtain

How this generator works

The flat width needed is the track plus the stack-back, times the fullness for that heading. Dividing by the fabric width less twelve centimetres of side hems gives the number of widths, rounded up — and rounded up again to an even number for a pair. The cut length is the drop plus twice the hem plus the heading allowance, then rounded up to a whole number of pattern repeats. The checks work back from the finished curtain: it must gather to at least the fullness the heading calls for, each cut must contain the drop and both allowances, each cut must be a whole number of repeats, and the metres must equal the widths times the cut length.

Randomness and fairness

Nothing is random. The same window and fabric always give the same answer.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

Side hems are taken as twelve centimetres a width, which is the usual allowance but varies by maker.
Lining and interlining are extra and are not counted here.
Half widths are not used; a maker may split one to save fabric.
Fullness ratios are the conventional ones and a particular heading tape may want more.

Privacy and your data

Window measurements are used only for the arithmetic in your browser, and are never uploaded or stored.