Fabric Yardage Is a Staircase, Not a Slope

The remainder is the whole story

Divide 140 by 46 and you get 3.04: three pieces fit and four hundredths of a piece is wasted. Divide 140 by 47 and you get 2.98 — still nearly three, and worth nothing, because you cannot cut ninety-eight per cent of a cushion front. That discarded fraction is where all the money goes. At 46 cm the bolt is 98.6 per cent used across its width; at 47 cm it drops to 67.1 per cent, and every row of the cut carries that waste down its whole length.

It follows that the sensitive number is not how much fabric you need but how close your piece width sits to a divisor of the bolt. A piece of 46 cm on a 140 cm bolt is on the good side of a step and a piece of 47 cm is on the bad side, and the difference between the two designs is a centimetre nobody would defend in a drawing. When a design has any latitude at all, spending it to land just under a divisor is the single cheapest optimisation in the whole craft.

What the model leaves to you

The calculation assumes every piece lies the same way up and that the fabric does not care which way it is turned. Neither is true of a print with a direction, a napped fabric like velvet or corduroy, or a check that has to match across a seam. A directional print forbids rotating a piece to fit, which can remove a whole column from a row; a nap forbids alternating pieces head to toe, which is the usual trick for packing a trapezoid. Add a quarter to the figure for a strong directional print and a third for a nap.

It also assumes the bolt width you type is usable width, and it usually is not. Selvedges are woven differently, often more tightly, and are frequently printed with the maker's name and colour dots; a bolt sold as 140 cm may give 136 cm of cloth you would actually cut into. Measuring the usable width on the piece you bought — not the width on the label — is the one input worth checking before the scissors come out.

Why a wider bolt is not always cheaper

For the twelve cushion fronts, moving from a 110 cm bolt to a 140 cm one cuts the length from 2.70 m to 1.80 m — a third less fabric. Moving on to a 150 cm bolt changes nothing at all, because three pieces of 45 cm still fit and a fourth still does not. The saving comes from crossing a step, not from the extra width itself, and paying more per metre for width that does not cross one is money spent on nothing.

The exception is a project with several different piece sizes, where a wider bolt gives the cutting layout more room to interleave. The calculator handles one size at a time, so for a mixed project run it once per size and add the results — that overestimates slightly, because it forbids nesting small pieces in the gaps left by large ones, and the overestimate is the right direction to be wrong in.

Frequently asked questions

How much fabric for twelve 45 cm cushion fronts?

1.80 m on a 140 cm bolt, 2.70 m on a 110 cm bolt and 0.90 m on a 280 cm one. Those are cutting lengths with no seam allowance and no allowance for a print, so add your seam allowance to the piece size before entering it — a 45 cm finished cushion with a 1.5 cm allowance is a 48 cm piece, which on a 140 cm bolt is already on the wrong side of the step.

Should I round the length up to the nearest half metre?

Yes, and most shops will do it for you anyway. Cutting is done by hand against a rule and a cut is rarely square to the selvedge, so the first straightening cut costs two or three centimetres before any piece is taken. Ten centimetres of insurance on a two-metre cut is four per cent and buys you a straight edge; it also covers the shrinkage of a cotton you prewash, which can take three per cent off the length.

Does the calculator handle a pattern with several piece shapes?

Not in one pass, and the honest answer is that no simple calculator can. Nesting differently shaped pieces on a fixed width is a packing problem with no closed-form answer, which is why professional cutting rooms use software and a marker. For home sewing, run one size at a time, add the results, and treat the total as an upper bound that a careful layout will beat by ten or fifteen per cent.