What this calculator works out
Curtain fabric is bought by the metre off a bolt of fixed width, so getting the order right comes down to two separate questions: how many widths of that bolt need joining together to gather up to the right fullness, and how long each of those widths has to be cut. This tool takes the track or pole width, the finished drop, a heading style and a fabric width, and turns those into widths per curtain, a cut length for every drop, and the metres (or yards) to order, lining included if the curtain is lined.
It covers the four headings most curtains are made to: pencil pleat, eyelet, pinch pleat and wave, each with its own typical fullness range, and both major fabric conventions: the 137cm (54in) standard decorator bolt used across the UK and US trade, and a 280cm wide-width option for a railroaded or seam-free fabric on a wide window. A pattern repeat is handled the same way it is on a roll of wallpaper: every cut length is rounded up to a whole number of repeats so the design lines up across every join.
How the maths works
Fullness is what turns a flat track width into a gathered curtain: a heading tape or hook system pulls in a set multiple of the track width to create the folds, so the fabric ordered has to be wider than the track itself. A pair of curtains is treated as two symmetrical panels, each covering half the track and each needing its own whole number of fabric widths joined side by side, since a width of fabric can't be split between two separate curtains.
Length works the same way the Wallpaper Calculator rounds a usable drop: the finished drop plus a fixed hem and heading allowance (turnings top and bottom) gives a plain cut length, and once a fabric has a pattern repeat, that cut length is rounded UP to the next whole multiple of the repeat, so the design sits at the same point on every width sewn into the curtain.
Lining reuses the same total-widths figure, since a lining bolt is usually a broadly similar width to the face fabric, but its own cut length skips the repeat rounding entirely: lining is plain, so there's nothing for a pattern to line up against.
A worked example
Take a UK bay window with a 240cm track, a 180cm finished drop to the sill, pencil pleat heading at the typical 2.25× fullness, a plain 137cm standard fabric and the default 25cm hem/heading allowance, made as a pair. Each curtain covers half the track, 120cm, gathered up to 120 × 2.25 = 270cm. One 137cm-wide fabric width doesn't quite cover that, so 270 ÷ 137 = 1.97, rounded up to 2 widths per curtain, 4 widths in total across the pair. Cut drop: 180 + 25 = 205cm, no repeat to round up to. Fabric to buy: 4 × 205cm = 820cm, 8.2m (about 8.97 yards), plus another 8.2m of lining at the same 4 widths. At a sample £18 a metre, the 8.2m of face fabric comes to about £147.60, before lining or making-up costs.
Swap in a fabric with a 32cm repeat on the same window: the cut drop jumps to the next whole multiple of 32cm above 205cm, which is 224cm (7 repeats), so fabric to buy becomes 4 × 224cm = 896cm, 8.96m, about 9% more than the plain fabric for exactly the same window. An American aside on the same track and drop, in inches: a 94.5in track (240cm), 70.9in drop (180cm), eyelet heading at 1.875× fullness, on a 54in (137cm) bolt: each curtain covers 47.25in gathered to 88.6in, needing 2 widths (88.6 ÷ 54 = 1.64, rounded up), 4 widths total, the same shape of answer a US maker would see from their own tape measure.
Heading styles and fullness
Pencil pleat and pinch pleat headings both typically run 2× to 2.5× fullness: enough fabric gathered into the tape or pleats to hide the track completely and give a soft, full stack when the curtain is open. Eyelet headings sit lower, usually 1.75× to 2×, since the rings themselves create soft, even folds without needing as much fabric pulled in behind them; too much fullness on an eyelet curtain can crowd the folds and make the pole hard to see. Wave headings, run on a gliding track with a fixed tape, typically sit at 2× to 2.2×, a narrower band because the tape's spacing is what creates the wave shape, not extra gathering. Every heading's fullness field on this page defaults to a mid-point figure and stays fully editable, since the exact look, and the exact fabric a maker is working with, both nudge the ideal figure a little either way.
Measuring the drop: sill, below sill and floor length
Where a curtain finishes changes both the look of a window and the length to measure. Sill-length curtains finish just short of the windowsill, about 1cm above it, so they clear without catching; below-sill curtains extend past it, typically finishing around 15cm below the sill, a length often chosen under a radiator or a low piece of furniture. Floor-length curtains run the full height of the wall, finishing about 1cm above the floor, close enough to skim it for a tailored look without the hem dragging, collecting dust or creasing underfoot. Every style starts the measurement from the same point: the top of the pole for an eyelet heading, since the curtain hangs directly off it, or the underside of the ring for every other heading style.
Fabric width and pattern repeat
137cm (54in) is the standard width for decorator and curtain-weight fabric on both sides of the Atlantic, the width most sample books and haberdashery ranges are cut to. A wide-width fabric, commonly around 280cm, is worth considering on a wide window: it can cover the whole gathered width in a single piece with no joins at all, at a higher cost per metre that's sometimes offset by needing fewer metres overall once joins are accounted for. Where a fabric has a pattern repeat, printed on the product label or spec sheet, this calculator adds it into the cut length as a planning allowance, the same rounding-up approach used for the Wallpaper Calculator's usable drop; a maker still lines the actual repeat up by eye against the real fabric on the cutting table.
Lining
A lined curtain hangs with more weight and body, blocks more light and protects the face fabric from sun fading, at the cost of an extra fabric bill. This calculator's lining figure reuses the same total-widths number worked out for the face fabric, since lining is typically sold on a comparable bolt width, but it's always cut plain, without the pattern-repeat rounding, since there's no design to line up on lining fabric. Toggling lining off removes it from the headline figure, the table and the chart entirely.
Questions people ask
How much fullness do eyelet curtains need?
Eyelet headings typically run 1.75× to 2× fullness, a touch less than pencil or pinch pleat, since the metal rings themselves create even, soft folds without needing as much fabric pulled in behind them. Too much fullness on an eyelet curtain can crowd the folds together and hide the pole; too little leaves the curtain looking flat and thin when closed.
How do I measure the drop for eyelet curtains?
Start at the top of the pole itself, not the ring or the track, since an eyelet curtain hangs directly off the pole through the ring holes. Measure straight down to wherever the curtain should finish, sill, below sill or floor length, and enter that figure in the finished drop field above.
Do I need lining?
Not always, but it's worth it on most living-room and bedroom curtains: lining adds weight and body to the hang, blocks more light and protects the face fabric from fading in direct sun. A lightweight voile or a curtain meant to filter light rather than block it is often left unlined on purpose.
What is railroading, and does it help on a wide window?
Railroading turns a fabric on its side, running the roll's width down the drop instead of across it, which lets a single wide-width fabric span a very wide window with no vertical joins at all. It only works on fabrics without a strong one-way pattern or pile, since railroading turns the design sideways too; check with the supplier before ordering a large plain or subtly textured fabric this way.
Why does a pair of curtains need a whole number of widths on each side?
Each curtain in a pair is sewn as its own panel, so the fabric widths joined into it have to be whole: a supplier can't cut half a width for one curtain and hand the other half to its neighbour. That's why this calculator works out widths per curtain first and doubles it for a pair, rather than splitting one combined total down the middle.
What allowance should I leave for hems and heading?
25cm (about 10in) combined, split roughly between a bottom hem and the top turning behind the heading tape, is a workable default for a full-length curtain. Shorter cafe-style curtains, or a fabric that frays less, can use a little less; a heavy interlined curtain sometimes uses more.
Fullness ranges, fabric widths and hem allowances on this page are drawn from published curtain-making guides, checked against two sources each where more than one was available: DotcomBlinds' and Scotts of Stow's measuring guides for drop styles and starting points, Direct Fabrics' and Livingstone Textiles' guides for heading fullness ranges, and Terrys Fabrics' and Jane Clayton's guides for hem and heading turning allowances. Every window has its own quirks, an uneven sill, a deep pole return, a fabric that behaves differently once it's hanging, so treat the figures here as a solid ordering estimate and check the fabric's own repeat and width against the label before cutting.