Craft & Making
Yarn Substitution Calculator
Enter original metres and weight, plus substitute metres per 100 g, to see balls and weight check.
Can I substitute this yarn?
Substituting yarn safely means matching total length first, then checking that the substitute’s weight for that length stays near the original so fabric density does not swing wildly. Enter the original project’s metres and grams, the substitute’s metres per 100 g, and ball size; the calculator scales metres with a buffer, converts to grams of substitute, and counts balls. Wraps per inch and needle advice still matter — this is a quantity and density cross-check, not a drape oracle. Swatch before committing a full sweater. Buy quantities with the yarn calculator once you lock a substitute, and compare put-ups via skein requirement.
Worked example
Original 1,200 m / 600 g → 200 m per 100 g. Substitute also 200 m/100 g in 50 g balls → metres/ball = 100; +10% need 1,320 m → 14 balls; ~660 g.
Limits and assumptions
Ignores fibre content, ply and recommended needle. Equal WPL can still feel different when spun differently.
Frequently asked questions
What is WPL?
Here WPL means wraps-style density expressed as metres per 100 g — how much length you get for a given weight. Closer WPL values usually substitute more cleanly than mismatched ones.
Why compare grams as well as metres?
Matching length keeps yardage honest; matching weight checks whether the fabric will be much denser or airier.
Can I substitute a different fibre?
Quantity maths still works, but drape, stitch definition and care may change — swatch.
What if metres per 100 g is missing?
Divide ball metres by (ball grams÷100) from the band.