Fabric is sold by length but cut by area
A bolt has a fixed width and unlimited length, so buying fabric means buying length. What you actually need is area, arranged in specific rectangles. Those two facts do not line up neatly, and the gap between them is why so many projects come up short: you converted an area into a length by dividing, when the real answer comes from counting how many pieces fit across the width and how many rows of them you need.
Start with the usable width. A 44-inch quilting cotton is 44 inches from selvedge to selvedge, but the selvedges themselves are woven more tightly, often carry pin holes and printing, and shrink differently from the body of the cloth. Trim half an inch from each side and you have 43 usable inches. On a printed cotton with a wide white selvedge band the loss can be an inch per side.
Then add the seam allowance. Pattern pieces are described by their finished size, but they are cut larger: 5/8 inch per edge is the commercial garment standard in the United States, 1 cm is the metric equivalent, and quilting works at 1/4 inch. A 12-inch finished piece with a half-inch allowance is cut at 13 inches, and it is 13 that has to divide into the usable width. That single inch is the difference between three pieces across a 43-inch cotton and only three across a 40-inch one.
Why the answer rounds twice, and why rotation sometimes wins
The calculation rounds in two places, both against you. Divide the usable width by the cut width of a piece and round down: three and a half pieces across means three, because half a piece is not a piece. Divide the quantity by that number and round up: eight pieces at three across needs three rows, and the third row holds only two. Between those two roundings, a project that needs 1,536 square inches of fabric ends up buying 2,468.
That is the origin of the utilisation figure, which is the net area of your pieces divided by the total area of fabric you buy. Sixty per cent is ordinary for large rectangles on a narrow bolt; ninety per cent is excellent and usually means your piece width divides the usable width almost exactly. Utilisation is not a mark of skill so much as a signal: a low number means there is a strip of usable fabric down one side of every row that you should be planning something into.
Rotating the pieces ninety degrees changes which dimension has to divide into the width, and it can change the answer dramatically. Six pieces 10 inches wide by 20 long, cut at 11 by 21, fit three across upright and need two rows of 21 inches — 42 inches of fabric. Turned sideways they fit only two across, but each row is 11 inches deep and three rows is 33 inches. The turned layout buys a quarter less fabric.
Rotation is not free. It puts the piece on the crosswise grain, which in a woven fabric stretches more than the lengthwise grain, and it is simply not permitted on a one-way print, a nap fabric such as velvet or corduroy, or a directional stripe. Leave the option off unless you have checked the fabric.
Worked example: eight 12 × 16 inch panels on 44-inch cotton
You are cutting eight tote-bag panels, each 12 inches wide and 16 inches long finished, from 44-inch quilting cotton at $9 a yard. You trim half an inch of selvedge from each side, sew with a half-inch seam allowance, and allow 10% for squaring the fabric and cutting error. The print is non-directional but you decide not to rotate pieces.
- Usable width. 44 − (2 × 0.5) = 43 in.
- Cut size of one piece. 12 + (2 × 0.5) = 13 in wide; 16 + (2 × 0.5) = 17 in long.
- Pieces across. 43 ÷ 13 = 3.31, rounded down to 3 across. The 4 inches left over on each row is offcut.
- Rows. 8 ÷ 3 = 2.67, rounded up to 3 rows. The third row carries only two pieces.
- Cut length. 3 × 17 = 51 in.
- Yards with waste. 51 ÷ 36 = 1.417 yd; × 1.10 = 1.56 yd (1.42 m). Ask the shop for a yard and five-eighths.
- Cost. 1.558 × $9 = $14.03.
- Utilisation. Net area is 8 × 12 × 16 = 1,536 in². Purchased area is 1.558 × 36 × 44 = 2,468 in². That is 62%.
Look at what the 38% is. Four inches down the side of every row, one inch of selvedge each side, and a third row that is only two-thirds full. If you also needed eight 4-inch pockets, they would come out of that side strip for nothing.
How to read the result and buy sensibly
Round the yardage up to the nearest eighth of a yard, because that is how fabric is sold at the cutting counter. A result of 1.56 yards is an order of one and five-eighths. Some shops cut only to the quarter yard; ask before you plan a layout that depends on an exact length.
Watch the quantity ladder in the results table. Yardage does not rise smoothly with quantity, it rises in steps of one row. With three pieces across, going from six pieces to seven costs you a whole extra row — 17 inches of fabric for one more panel. If you are near a step, cutting the ninth piece is free while cutting the seventh is expensive. This is the single most useful thing the table tells you.
Treat the waste allowance as covering three specific things: squaring the cut end, which is rarely straight off the bolt; straightening the grain, which can cost several inches on a badly rolled fabric; and cutting error. It does not cover shrinkage. If the finished item will be washed, either pre-wash the fabric before cutting — which is the reliable answer for cotton and linen — or add the manufacturer's stated shrinkage on top, typically two to five per cent for woven cotton.
Nor does it cover pattern matching. A fabric with a repeat that must align across a seam needs extra length on every piece, in exactly the way described in the curtain fabric calculator, where the vertical repeat can add a fifth to the total. If your fabric has a large repeat, calculate the yardage here and then add one repeat per row.
Standard fabric widths and what is usable
| Fabric type | Nominal width | Typical selvedge loss (each side) | Usable width |
|---|---|---|---|
| Quilting cotton | 42–44 in | 0.5 in | 41–43 in |
| Apparel cotton, poplin, shirting | 45 in | 0.5 in | 44 in |
| Decorator and drapery fabric | 54 in | 0.5–1 in | 52–53 in |
| Apparel knits, jersey | 58–60 in | 0.5 in | 57–59 in |
| Wide-back quilting cotton | 108 in | 0.5 in | 107 in |
| Wide sheer / voile | 118 in | 0.5 in | 117 in |
| Interfacing (fusible woven) | 20–22 in | 0.25 in | 19.5–21.5 in |
Widths vary by mill and by run. Measure the bolt end rather than trusting the label if the layout is tight — a 44-inch cotton that arrives at 42 costs you a whole piece per row.
Assumptions this calculator makes, and where they break
- Pieces are rectangles. A shaped garment piece is calculated by its bounding rectangle, which overstates the fabric slightly for a curved piece and considerably for an L-shaped one. For real garment layouts, a pattern envelope's yardage chart accounts for nesting that no rectangle model can.
- All pieces are the same size. Run the calculator once per distinct piece size and add the cut lengths, then apply the waste allowance to the total.
- Grain is respected. The upright layout puts the piece length along the fabric length, which is the lengthwise grain. Rotation trades that for the crosswise grain.
- No pattern matching. A directional or repeating design needs extra length on every row and often forbids rotation entirely.
- No shrinkage. Pre-wash washable fabric before cutting, or add the stated shrinkage on top of the calculated yardage.
- No fold layout. Cutting a piece on the fold uses half the usable width for a piece twice as wide; enter the full opened-out piece width and turn off rotation to model that case.
- Offcuts are ignored in the total. The side strip left on each row is real fabric. Plan pockets, facings, bindings and pouches into it before you buy more.
Related layouts and when a different tool is right
This calculator answers the general case: identical rectangles on a bolt of known width. Several common jobs have their own arithmetic, because the constraint is different.
Quilt backing is the case where the whole surface is one large piece and the only decision is which way the seams run; that comparison, including the wide-back option, is the job of the quilt backing yardage calculator. Binding and other continuous strips are the opposite case: many long narrow strips joined end to end, where the count of strips rather than the layout drives the yardage, which the quilt binding calculator handles. Curtains have their own rule because the fabric requirement is set by a fullness ratio rather than by piece dimensions, which is what the curtain fabric and fullness calculator does.
For patchwork units, the piece size itself is derived rather than given, because triangles and squares change size when they are sewn. The half square triangle calculator gives you the cut size to feed into this one.
Commercial cutting rooms solve a harder version of the same problem, called marker making: nesting irregular shapes across a width to maximise utilisation across dozens of sizes at once. Utilisation in the high eighties is considered good in production apparel. If your utilisation here is far below that on simple rectangles, the fix is almost always a different fabric width rather than a cleverer layout.