How Much Fabric Do I Need for Curtains?

Curtains are the project most likely to blow a fabric budget, because they use long lengths and because the arithmetic has a twist that a simple area calculation misses: curtain fabric is joined in whole widths. This guide walks through a full example, from measuring the window to the length to order, using the site's Fabric Yardage Calculator and Fabric Shrinkage Calculator, and shows where the quick area-based estimate and the real number part company.

Measure the track or pole, not the window

Curtain width is based on the length of the track or pole, because the curtains hang from it and usually extend beyond the window frame so they can be drawn clear of the glass. Measure the full length of the track or pole, excluding decorative finials. The drop is measured from the point the curtain hangs from, such as the track runners or the pole rings, to where you want it to finish: sill, below the sill, or floor.

For the example here: a track 180 cm long, and a finished drop of 230 cm.

Fullness: why curtains need more width than the track

A flat curtain the width of the track would look like a sheet. Curtains are gathered or pleated by the heading, and the amount of extra fabric is called fullness. It depends on the heading style and on the heading tape's instructions. Fullness of about twice the track width is common for many gathered and pencil-pleat headings; some styles use more, some less. Check the tape or the heading you plan to use.

At twice fullness, the 180 cm track needs 360 cm of finished curtain width in total, shared between the pair. Add allowances for side hems as your heading guidance recommends; this example keeps them inside the figures for simplicity.

The cut drop

Each width of fabric must be cut longer than the finished drop, to allow for the heading at the top and the hem at the bottom. Allowances vary with the heading and hem style; a total of around 20 to 30 cm is common for a lined curtain with a deep double hem. Here we add 25 cm, so each cut drop is 230 + 25 = 255 cm.

Number of widths

Curtain fabric commonly comes in widths around 137 to 150 cm. Suppose it is 137 cm, with about 132 cm usable after trimming the selvedges for seams. To make 360 cm of curtain, you need 360 ÷ 132 = 2.73 widths, and you cannot buy 0.73 of a width in any useful way: round up to 3 widths. For a pair, that is usually one and a half widths per curtain, with the half width placed at the outer edge.

So the fabric to buy is 3 cut drops of 2.55 m: 7.65 m.

What the area method says

For comparison, enter the area into the yardage calculator. The fabric needed is 3.6 m of finished width by 2.55 m of cut drop, 9.18 m². With 132 cm usable width:

• with no waste allowance, the calculator gives 6.95 m;
• with a 10% waste allowance, it gives 7.65 m.

Here the 10% allowance happens to land on exactly the right answer, because the rounding up from 2.73 to 3 widths is about 10%. That is a coincidence of this example, not a rule. With a different track width you might need only 2.1 widths, rounding up to 3, a 43% jump that no ordinary waste allowance would cover; or 2.95 widths, rounding to 3 with almost no waste. For curtains, always count whole widths. The area method is useful as a cross-check, and for linings and interlinings that are sometimes pieced differently.

Pattern repeats

A patterned fabric has to match across the joins between widths and line up between the two curtains. That means each cut drop must start at the same point in the pattern, so each drop is rounded up to a whole number of pattern repeats. If the pattern repeats every 64 cm, a 255 cm drop needs four repeats, 256 cm, and in practice you also need to choose where the pattern sits at the top or hem, which can add up to one more repeat per drop. On long drops with large repeats this adds up quickly; ask the supplier for the repeat and work it out before ordering. Plain fabrics and small all-over prints avoid this.

Shrinkage

Curtain fabric is often not washed, but if it will be, or if it is a cotton or linen that may shrink when steamed or cleaned, allow for it. With 4% shrinkage, the shrinkage calculator's pre-cut mode turns the 255 cm cut drop into 265.63 cm, and the full 7.65 m order into 7.97 m. Test a sample first; the guide to measuring shrinkage explains how. Linings may shrink at a different rate from the face fabric, which can make a curtain pucker or the lining droop below the hem after cleaning; many makers recommend matching the care method of lining and face fabric.

Linings and interlinings

Linings protect the face fabric from sunlight, improve drape and add some insulation. Blackout linings block light. Interlinings, a soft layer between face and lining, add body and warmth. They are usually cut slightly shorter than the face fabric, and the same width rule applies: count whole widths of the lining's own width.

Weight on the track

Long, lined and interlined curtains are heavy. The Fabric Weight from Dimensions tool gives a quick figure: enter the GSM, the total length and the width for each layer and add them up. Check that the track or pole, its brackets and the wall fixings are rated for the weight, especially on plasterboard walls.

Lining quantities

Linings follow the same rules as the face fabric, with two differences. Lining fabric often comes in a different width from the face fabric, so count whole widths of the lining's own usable width. And linings are usually cut a few centimetres narrower and shorter than the face, because they finish inside the side turnings and above the hem. If the curtain lining in this example came at 137 cm with 132 cm usable, the same three widths would be needed; at a 150 cm lining width with 145 cm usable, 360 ÷ 145 = 2.48, still three widths, so in this case the wider lining saves nothing. Blackout linings are heavier than standard linings and add to the load on the track. Interlinings come in wide widths in some ranges, which can reduce the number of joins. Work out each layer separately; the totals are rarely the same as the face fabric's.

Safety

• Cords and chains. Looped cords and chains on curtains and blinds can strangle young children. Keep cords out of reach, use cord tensioners or tidies fixed to the wall, or choose cordless systems. Many countries have specific safety rules for window coverings with cords.
• Fire. Keep curtains clear of heaters, fires and candles. Curtains in workplaces, rental properties and public buildings may need to meet fire-safety rules; if that applies, buy fabric certified for it and keep the certificate.
• Heavy curtains need secure fixings; a falling pole is a hazard.

Summary of the example

• Track 180 cm, twice fullness: 360 cm of finished width.
• Drop 230 cm plus 25 cm allowances: 255 cm cut drop.
• Fabric 132 cm usable: 2.73 widths, rounded up to 3.
• Order: 3 × 2.55 m = 7.65 m, plus pattern repeat if any, plus shrinkage allowance if washing (7.97 m at 4%).

The yardage calculator gives a fast estimate from area; for curtains, check it against the whole-width count, and when they disagree, buy by whole widths.