Yarn substitution calculator
When a yarn is discontinued or unavailable, match it by length, not by weight. Enter what the original project used and the put-up of the replacement.
Why length, not weight
Two 100 g skeins can hold wildly different amounts of yarn. A dense woollen-spun yarn might give 160 m per 100 g; a fluffy blown yarn might give 300 m. If you substitute by weight, you can end up several skeins short — or holding a lot of leftover yarn.
The calculator works in metres because metres are what the fabric consumes. Total length is then divided by the replacement skein length and rounded up, with a buffer for swatching, tension differences and dye lots.
The formula
total length = original length per skein × skeins used
replacement skeins = ⌈ total length × (1 + buffer) ÷ replacement length per skein ⌉
Matching more than yardage
Length gets you the right quantity. These three checks get you the right fabric:
- Gauge band. Stay within one weight category, or swatch and change needle size deliberately. A DK substituted for worsted will knit to a different fabric at the same needle.
- Fibre behaviour. Replacing wool with cotton changes drape, memory and weight. Cotton is heavier per metre and does not bloom after blocking.
- Ply and texture. A smooth plied yarn will not mimic a haloed mohair or a chainette. Match the structure if stitch definition matters.
Worked example
A pattern calls for four skeins of a discontinued yarn with 183 m per 100 g skein: 732 m total. With a 10% buffer you need 805 m. The replacement offers 200 m per 100 g skein, so 805 ÷ 200 = 4.03, rounded up to 5 skeins — about 500 g. Without the buffer you would buy 4 skeins and run out during the final sleeve.
Questions
Can I substitute a different weight?
You can, but treat it as a new project. Swatch to the pattern gauge, expect the fabric to change, and recalculate yardage from the new gauge rather than trusting the original figure.
Should I buy the same dye lot?
Yes, for anything larger than a small accessory. Buy all skeins at once and keep the labels; the calculator's buffer exists partly to cover a late extra skein in a mismatched lot.
Why is the estimated weight different from the original?
Because the replacement has a different length per 100 g. The fabric needs the same metres, not the same mass. The weight figure is only a shipping-and-stash estimate.
Put-up figures in the library come from manufacturer specifications and are dated on each yarn page. Always confirm against the label before buying a full project quantity.