A good substitute matches the original where it counts: thickness (the label’s density tells it), gauge (the swatch confirms it), and total yardage (never total skeins). Enter both yarns; the verdict comes reasoned, not just colored.
The Two Yarns
From each label: grams and yards per skein.
Verdict
Good match
substitute runs 9% heavier (thicker)
Thickness matches. Swatch at the pattern’s needles, expect gauge within half a stitch, and buy by the yardage line above.
- Pattern yarn220 yd / 100 g
- Substitute200 yd / 100 g
- Difference-9.1%
- Skeins of the substitute7 · buy 8
The Checks
density = yards per 100 g, compared: within ±10% reads as the same thicknessbuy by total yards: skeins = pattern’s yards ÷ substitute’s yards per skeinDensity is the label’s honest thickness measure: two “worsted” labels can differ by a quarter. The ±10% window is the working rule; outside it, the substitute knits a different fabric at the pattern’s needles, and inside it the swatch still gets the final word.
Worked Example
Pattern yarn 100 g / 220 yd (1,300 yd needed); substitute 100 g / 200 yd, same fiber family:
- Densities: 220 vs 200 yd per 100 g, the substitute gives 9% fewer yards per gram: inside the window, on its thick edge.
- Buy: 1,300 ÷ 200 = 6.5 → 7 skeins, buy 8: one more than the pattern’s yarn would need.
- Swatch expecting a half-stitch-tighter gauge, and go down a needle if the fabric boards up.
Beyond the Numbers
- Fiber changes behavior at equal thickness: alpaca grows and drapes, cotton neither stretches nor forgives, superwash relaxes. The fiber menu shades the verdict.
- Ply and spin matter for texture: a 2-ply lace shows cables poorly however right its grams; check the stitch the pattern leans on.
- Color changes the pattern: variegated substitutes hide texture patterns completely. Not arithmetic: still true.
Assumptions and Defaults
- ±10% density reads as a match, 10–20% as swatch-and-decide, beyond as a different weight class (the held-together trick sometimes rescues a too-thin favorite).
- Skeins round up plus the dye-lot spare.
- Meters-labeled yarns convert at 1.0936, or let the conversion calculator feed this one.
Substitution Questions, Answered
How do I know if a yarn can substitute for another?
To know whether a yarn can substitute for another, compare the yards per 100 g on both labels, since within 10% means the same thickness, then swatch for gauge, and finally buy by total yards. Those three checks work best in that order, and the example pair passes at 9% apart.
Why buy substitute yarn by yards rather than by skeins?
You buy substitute yarn by yards because skeins differ in length: the pattern’s eight 220 yd skeins hold 1,760 yards, so a 200 yd substitute needs nine. Matching skein counts instead of yards is how a substitution ends up one sleeve short.
Can I substitute yarn across fiber types?
Yes, you can substitute yarn across fiber types, as long as you expect the fabric to change: cotton in place of wool is stiffer and loses its stretch, alpaca grows and feels warmer, and acrylic washes easily but barely responds to blocking. The density can match while the garment’s character changes, so swatch, wash the swatch, and only then commit.