How to Calculate Fabric for Curtains

The most expensive mistake in curtain making is ordering half a yard short on a fabric you love. Ten yards of patterned drapery at forty dollars a yard is four hundred dollars on the table, and the remaining half yard you need might be from a different dye lot or a different bolt entirely, with the pattern placed a centimetre off. The fix for this is arithmetic. Once you understand what the numbers do, curtain fabric stops being an anxious guess and becomes a decision you make with confidence.

This guide walks through every step of the calculation in the order you actually face them: measuring the window, choosing a heading, deciding on pattern and lining, and handling odd shapes like bay windows. A curtain fabric calculator handles the arithmetic in seconds, but understanding what is happening inside it is how you catch errors before you hand money to the fabric shop.

Start with the Track, Not the Window

Every curtain calculation starts from the curtain track or pole, not the window itself. The window tells you very little about how much fabric you need. The track tells you everything. A 48-inch window with an 8-inch stack-back on each side has a 64-inch track, and 64 is the number that feeds every subsequent step.

Before you pick up a tape measure, the fittings should be in place. You cannot measure a track that has not been installed yet, because the position of the track determines both the width and the drop. If you are working from a plan, measure the plan — but the moment the fittings go up, measure again.

Here is what to measure, in order:

• Track or pole width. Measure the full span end to end, including any extensions beyond the window frame that allow the curtains to stack clear of the glass when open. A standard stack-back is around a third of the window width split across both sides.
• Finished drop. Measure from the top of the heading (where the curtain attaches to the track or rings) down to where you want the bottom hem to fall. For sill-length curtains, stop at the sill. For floor-length, stop 1 cm above the floor. For puddling, add 5 to 15 cm depending on how much fabric you want pooled.
• Returns. On tracks with returns — the short section that wraps from the front of the track back to the wall — add the return measurement to each end of the total width. Returns prevent light gaps and give a finished look from an angle.

Measure twice. A 2 cm error in track width might not matter on a 300 cm track, but a 2 cm error in drop multiplies across four or more fabric widths, and suddenly your floor-length curtains finish an inch off the floor. If you are buying fabric for multiple windows, measure each one separately — builders’ tolerances mean no two windows are truly identical.

The Heading Decision Doubles or Triples Your Fabric

Heading style is the single biggest fabric decision you will make. A tab-top curtain and a goblet pleat curtain on the same track can differ by two times in total fabric, because each heading requires a different fullness ratio — the multiple of track width that feeds the gathering.

Fullness is what makes curtains look like curtains rather than flat sheets hung at the window. A ratio of 2 means using twice as much fabric as the track width; 2.5 means 150 percent more fabric than flat. The ratio is applied before you even think about drop, because it multiplies the number of fabric widths you need.

These are the common headings and their fullness requirements:

• Pencil pleat uses 2 to 2.5 times fullness. The heading tape creates narrow, regular gathers. Two times is standard; 2.5 times gives a richer look at a modest fabric premium.
• Pinch pleat uses 2.5 times fullness. Fabric is pinched into groups of two or three pleats at regular intervals, producing a tailored heading.
• Eyelet or grommet uses 2 times fullness. Metal rings punched through a reinforced header create bold, even folds.
• Tab top uses 1.5 times fullness. Fabric loops sewn to the top hang flat between tabs, so the fabric total is smaller — but the look is casual rather than formal.
• Goblet pleat uses 2.5 to 3 times fullness. Each pleat is shaped into a goblet and often stuffed with wadding. This is the fabric-hungriest heading in common use, and it shows.

To put numbers on it: a 60-inch track at 2 times fullness needs 120 inches of gathered fabric. At 3 times, the same track needs 180 inches — a 50 percent increase before pattern repeat or hems enter the conversation. The fullness you pick is both a design choice and a budget choice, and the two should be made together.

How Many Fabric Widths You Actually Need

Once you know the total gathered width, you divide by the usable fabric width to work out how many widths of fabric each panel needs. You cannot use a partial width — each panel is sewn from complete widths joined at the seams. Our standard fabric widths guide covers which widths you can expect from which types of fabric.

Say you have a 60-inch track, two panels, and 2 times fullness. Gathered width per panel is (60 ÷ 2) × 2 = 60 inches. On 54-inch drapery fabric, each panel needs two widths (you round up — 60 divided by 54 is 1.11, and you cannot buy 1.11 widths). Two panels at two widths each is four widths total.

This rounding is where fabric totals can feel surprising. A 55-inch gathered width and a 54-inch fabric both give you two widths per panel, because you cannot cut 1.02. Slight differences in track width or fullness ratio can push you from one width to two, which doubles the fabric cost for that panel. Check the arithmetic before committing — sometimes shifting from 2 times to 2.25 times fullness changes nothing in the width count but gives you a fuller curtain.

Pattern Repeat Is Where the Waste Lives

Patterned fabric costs more than plain fabric even at the same price per yard, because pattern matching requires waste. Every drop of fabric has to be cut at the same point in the pattern so that stripes, florals, or geometrics line up when widths are sewn together.

The rule is simple: your cut drop rounds up to the next whole pattern repeat. If the cut drop is 96 inches and the repeat is 12 inches, 96 is already a multiple of 12, so no waste. If the cut drop is 97 inches, it rounds up to 108 — eleven inches of waste per width. Multiply that by four widths and you have nearly 44 inches — more than a yard — of waste fabric.

The larger the repeat, the more waste. A fabric with a 24-inch repeat can add several yards of waste to a modestly sized window. This is why interior designers often recommend plain fabric for first-time curtain makers: the numbers are more forgiving, and the margin for error is smaller. For a full explanation of how repeats work — including half-drops, where alternating columns are offset — see our understanding pattern repeat guide.

Half-drop repeats do not change the fabric total, despite looking visually more complex. The cut drop still rounds up to the next full vertical repeat. What changes is the cutting layout: every other width is shifted down by half the repeat distance so that the pattern aligns across seams. If you are used to standard repeats, a half-drop needs careful marking before you cut, but the yardage calculation is identical.

Hems and Heading Allowance

Every cut drop includes more than the finished drop. You need fabric for the bottom hem (usually a double fold, which eats four inches) and for the top heading (which varies with heading style). A standard total allowance is 12 inches — 6 inches for a double-fold bottom hem and 6 inches for the heading.

Deeper allowances apply to specific headings. Pinch pleats need about 8 inches at the top because the pleat tape is deeper; goblet pleats may need 10 inches. Eyelet headings can work with as little as 4 inches because the fabric folds from the grommets rather than from a tape. Cafe curtains with a single-fold bottom hem can manage on 8 inches total.

Add the allowance to your finished drop before you apply the pattern repeat. If your finished drop is 84 inches and your allowance is 12 inches, your cut drop is 96 inches. Only then do you round up to the next pattern repeat. Working in the wrong order produces wrong answers.

Lining — and Why It Is Usually a Separate Calculation

Lined curtains drape better, block more light, and insulate the window. Blackout lining adds weight and opacity. But lining is not a multiplier on your main fabric total — it is a separate calculation on its own fabric width.

Lining fabric is usually sold at a standard width (often 54 inches in the UK, 45 inches in parts of the US), so the number of lining widths may differ from the number of face fabric widths. If your face fabric is 54 inches wide and your lining is 45 inches wide, a 60-inch gathered panel still needs two widths of face fabric — but it also needs two widths of 45-inch lining, not one. Check each width separately.

Lining drop is usually an inch or two shorter than the face fabric drop, because the lining hem is attached above the curtain hem rather than level with it. It also does not have pattern repeat considerations, because lining is plain. For most curtains, the total lining yardage works out close to the total face fabric yardage, but the two should be calculated independently.

Bay Windows and Awkward Shapes

Three-panel bay windows are the most common complication. The principle stays the same — track width times fullness, divided by fabric width — but the track is longer and typically divided into three sections with two overlaps or meeting points.

Measure the full length of the curved or angled track as one continuous measurement. Do not measure each section separately unless each section has its own track. For a bay window with a single curved track, set the panel count to three in your curtain calculator and enter the full track length. The calculator divides the fabric across three panels.

Curved bay tracks need extra consideration at the curves. Fabric bending around a curve needs more width to hang cleanly — some makers add 10 percent to the gathered width calculation on deeply curved bays. If your bay is shallow, this is usually unnecessary.

A Worked Example from Start to Finish

Here is how the full calculation runs on a real window. The window is a 60-inch-wide living room window with a pole extending 6 inches beyond the frame on each side, giving a 72-inch pole width. The finished drop is 92 inches. The fabric is 54 inches wide with a 16-inch vertical pattern repeat. The heading is pencil pleat at 2.5 times fullness. Hem allowance is 12 inches. Plain lining, 54 inches wide.

Gathered width per panel: (72 ÷ 2) × 2.5 = 90 inches. Fabric widths per panel: 90 ÷ 54 rounds up to 2. Two panels at 2 widths each: 4 total widths.

Cut drop before repeat: 92 + 12 = 104 inches. Rounded to the next 16-inch repeat: 112 inches (seven full repeats).

Total face fabric: 4 widths × 112 inches = 448 inches = 12.44 yards. Rounded up to the nearest one-eighth yard: 12⅝ yards.

Lining runs the same width and widths count, but without the pattern repeat penalty. Lining cut drop: 92 + 12 = 104 inches. Total lining: 4 × 104 = 416 inches = 11.56 yards. Rounded up to 11⅝ yards.

Total fabric for the project: 12⅝ yards of face fabric plus 11⅝ yards of lining. The pattern repeat added 8 inches to every cut, or 32 inches (nearly a yard) of waste across four widths. That waste is the price of a matched pattern.

Ordering, Cut Lengths, and the Shop Conversation

Once you have the numbers, the fabric shop conversation is simple. Tell them the total yardage, the width you need, and the specific fabric. Most shops will cut a single length unless you ask otherwise. On patterned fabric, confirm the repeat before they cut — a helpful assistant will measure the repeat with you and count drops.

If your total is 12⅝ yards, ask for exactly that. Shops usually cut to the nearest eighth of a yard on a standard-price bolt and to the nearest quarter on remnant or sale bolts. Metric shops cut to the nearest 10 cm. Do not accept a cut that is shorter than your calculation — the assistant measuring fabric on a roll can be off by an inch or two, and an inch short on one drop can ruin the pattern match across seams.

Check the fabric for flaws before you leave the shop. Faults are marked on the selvedge with coloured string or a paper flag, and the shop will usually allow extra at a flaw or give a discount. Unmarked flaws discovered at home are harder to resolve after the fact.

Where People Go Wrong

A handful of mistakes account for most curtain-fabric disasters. Avoiding them costs nothing but attention.

• Measuring the window instead of the track. This is the most common error and produces curtains that will not close properly.
• Underestimating fullness. Heading tape designed for 2.5 times fullness will not pleat properly at 1.8 times. The tape will be visible, the pleats will collapse, and the curtain will look wrong.
• Forgetting hem allowance. A cut drop that equals the finished drop produces curtains with no heading and no hem — which is to say, raw fabric edges at top and bottom.
• Splitting a width between panels. Each panel is built from complete fabric widths. Leftover fabric from one panel cannot be used on another.
• Buying across multiple dye lots. Fabric from different bolts can vary noticeably in colour, and the pattern placement can shift between print runs. Order everything at once, from one supplier, if you possibly can.
• Ignoring shrinkage on cotton. Untreated cotton can shrink 3 to 5 percent on first wash. If your curtains will be washed in future, pre-wash the fabric before cutting, or add a shrinkage allowance.

If any of this feels complex, it helps to remember that curtain fabric is one of the few projects where the calculation fully determines the result. Get the numbers right and the curtains will hang as planned. The general fabric yardage calculator is useful for pieces and garments, while the dedicated curtain calculator applies fullness and pattern repeat automatically. If your project needs a different window treatment, the roman blind fabric calculator handles blinds where fullness does not apply but fold allowance does. And if the same pattern repeat concept applies to your quilting work, the quilt backing calculator uses similar logic for backing panels.

Fabric shops in different countries quote in different units. If your supplier is in one system and your plan is in another, the yards to metres converter handles the arithmetic. Start with the track, work through heading and pattern, and every curtain project becomes the same kind of problem — which means you can solve it every time.