The pattern wants 45 inch fabric. Yours is 60. How do you convert?

Every fabric width conversion chart is the same piece of math: 60 inch fabric is a third wider than 45, so you need about a quarter less length. As a starting point that works. But pattern pieces are not liquid, and when one of them stops fitting the new width, the chart misses by a full yard. Here is the chart, and here are its failure modes.

The conversion chart

The 1, 2 and 2.5 yard rows are as published by Sew4Home; the other rows are the same multiplication carried on. Read left to right when your fabric is wider than the pattern assumes, right to left when it is narrower. Historical Sewing works a larger example with the same ratio: 10 yd at 45 in converts to about 8 1/8 yd at 60 in.

The metric version of the problem is 140 cm versus 110 or 90 cm. A Swiss yardage table (Trendschnitt) states the same ratio from the other side: starting from a 140 cm figure, plan roughly 50 percent more on 110 cm fabric and nearly double on 90 cm.

Why an area ratio works at all

You are buying area. A yard of 60 in fabric holds a third more square inches than a yard of 45 in, so if the pattern's total area stays constant, the length shrinks by the inverse ratio. Most garment pieces are narrower than about 20 in, and narrow pieces re-flow into a wider fabric roughly the way text re-flows into a wider column: same content, shorter column. As long as every piece is comfortably narrower than both widths, the ratio holds to within a small remainder.

Where the chart breaks

Going narrower, the failure is a piece that no longer fits across. A wide pant leg, a bodice cut on the fold, a half-circle skirt panel: pieces in the 20 to 30 inch range sit two across on 60 in fabric and refuse to pair on 45. Every piece that stops pairing claims its own length of fabric, and the requirement jumps far past the chart's 1.33. The circle skirt is the extreme case, dramatic enough that we gave the cliff its own guide: a skirt that fits the width in one piece on 150 cm goods becomes two half circles and more than double the fabric on narrower goods. And a piece wider than 45 in in every orientation does not convert at all. It needs re-piecing, and no chart will warn you.

Going wider, the chart fails politely but expensively: it promises savings that never arrive. If your pieces happened to fill 45 in cleanly, say two 22 in panels side by side, the extra 15 in on a 60 in bolt may be too narrow to hold any further piece. You buy nearly the same length as before, the chart said a quarter less, and the difference is a strip of expensive selvage-to-nothing. This is the sense in which a conversion chart can be off by a full yard in either direction: it does not know your shapes.

The chart's own fine print

Sew4Home attaches two caveats worth repeating. Directional prints and large motifs need extra fabric on top of any converted figure (the one-way guide covers how much), and "when in doubt, add an extra 1/2 yard." That last line is the chart admitting, honestly, that it cannot see your pieces.

The correct conversion is a re-layout

The only conversion that cannot mislead you is laying your actual pieces into the actual width and reading the length. On the floor with painter's tape, or digitally in seconds per width.