Curtain Calculator

How Does the Formula Work?

This calculator works out how much curtain fabric to buy for one or more windows. Enter the length of the track or pole, the finished drop, the fullness you want, how many windows you are dressing, the width of the fabric on the roll and its pattern repeat. You get the fabric in metres and in yards, the flat width of the curtains, how many fabric widths to cut, the length of each cut and the extra length that pattern matching costs.

What the Calculator Assumes

Every window gets a pair of curtains, so the curtain width is split in two and each half is worked out on its own. Each curtain gives up 8 cm to a turn on both side edges, each fabric width loses 3 cm of selvedge, and each drop carries 20 cm for the top and bottom hems. These allowances are the tool's own working figures, not a standard, so a workroom that uses different ones will arrive at a slightly different total. The fabric is always cut along the roll, one width per drop, and wide sheer fabric is treated the same way. The result covers the face fabric only; lining, interlining and heading tape are bought separately.

Fullness

Fullness says how much wider the flat fabric is than the track it hangs from. At 2× a 200 cm window takes 400 cm of curtain, which gathers back to 200 cm once the heading is pleated. The calculator offers 1.5×, 2×, 2.5× and 3×. Which one is right depends on the heading: tapes, eyelet systems and pleat systems are each made for a particular fullness, so use the figure printed on the tape or given by the maker of your track.

Fabric Width and Pattern Repeat

The fabric width list offers 140 cm (55 inches), 150 cm (59 inches) and 280 cm (110 inches). A wider roll means fewer widths: the 200 cm example above needs 4 widths of 140 cm fabric but only 2 of 280 cm fabric, which halves the order to 5.2 m. Pattern repeat is the distance down the fabric before the design begins again. Each drop is lengthened to a whole number of repeats so the design lines up across the seams, and that extra length is the pattern waste. With a 64 cm repeat the 260 cm cut grows to 320 cm, 60 cm of waste on every width, and the same window needs 12.8 m. Enter 0 for a plain fabric.

Measuring

Measure the track or pole rather than the glass, because that is what the curtains hang from. For the drop, measure from the point the curtain will hang from down to where you want it to stop. Floors and sills are seldom perfectly level, so take the drop in more than one place and use the longest figure.