Yarn Requirement & Substitution
Skeins to buy from what a pattern asks for — a length, a weight or skeins of its yarn — with your margin, and how a substitute yarn compares by length per gram.
The yarn length and weight the project needs including your margin, the skeins of the yarn on your label and what is left over, and for a substitute its skeins, weight and how its length per gram compares.
Example: 1,200 yd plus 10 % is 1,320 yd: six 220 yd / 100 g skeins (600 g); a 210 yd / 50 g substitute runs 91 % longer per gram — 7 skeins, and a different thickness to swatch.
Length is
the common unit.
How a requirement stated three ways becomes one length, what the skein label contributes, how the substitute is judged, and why the margin is yours.
One length
A pattern states its yarn as a length, a weight or a number of skeins of the yarn it was written for. Length is the figure that survives a change of yarn, so the page turns the other two into a length using the original yarn’s label: weight × (skein length ÷ skein weight), or skeins × skein length. The margin you allow is added as a percentage, and skeins to buy are the length divided by the skein length, rounded up; the remainder is what stays in the bag.
Substitution
A substitute is judged by the same length: its skeins from its own label, and its weight. Length per gram is the label’s nearest proxy for thickness — two yarns with similar yards per gram are usually a similar weight class, and one that runs much longer per gram is finer. The page flags a difference beyond 10 % and says nothing about fibre, twist or gauge, which only a swatch settles.
Margin
Dye lots differ, tension differs between knitters, and a skein short at the end cannot be matched later. The margin is yours to set; none is assumed, and the page says so when it is zero.
What the number does not settle
How much yarn a garment size needs when the pattern gives no figure, yarn weight categories, and gauge are outside this page — see Knitting Gauge Converter for the swatch. Inputs stay in your browser; the same anonymous usage counts as the rest of the site apply.