Yarn Substitution Calculator
Patterns specify yarn by total length because that is what determines whether you have enough to finish. When you swap the recommended yarn for a different brand or fibre, the number of balls rarely matches one to one: each yarn puts a different length on its ball. This calculator finds the total length your pattern needs, then tells you how many balls of your chosen substitute yarn cover it. Enter the original yarn's ball count and length per ball, plus your substitute's length per ball, to get the number of balls to buy. Always check gauge separately with a tension swatch.
Yarn substitution formula
Total length = original balls * original length per ball
Exact balls = total length / substitute length per ball
Balls to buy = round up (exact balls)
Surplus = (balls to buy * substitute length) - total length
Substituting by total length is the standard method recommended by yarn manufacturers and craft guilds. The figures you enter come from the ball band of each yarn, so nothing here is assumed. Round up so you never fall short, and treat surplus as your safety margin.
Yarn substitution tips
- Read the length per ball off the ball band: it is usually printed in both metres and yards (1 yard = 0.9144 m).
- Match yarn weight category (lace, fingering, DK, worsted, bulky) so the gauge is close before you start.
- Knit a tension swatch and block it before measuring; fibre content changes drape and stretch.
- Buy all balls from one dye lot where possible, and one extra for safety.
- For colourwork or stripes, calculate each colour separately using its own pattern length.
Yarn substitution: frequently asked questions
How do I substitute one yarn for another?
Match by total length, not by ball count or weight alone. Find the total length the pattern requires (number of balls times the length per ball of the original yarn), then divide that total by the length per ball of your substitute yarn and round up. Always also check that the substitute yarn knits to the same gauge or tension, otherwise the finished size will differ.
Why can't I just buy the same number of balls?
Different yarns put different lengths on a ball even at the same weight. A 50 g ball of one DK yarn might hold 120 m while another holds 145 m. Buying the same number of balls can leave you short or with surplus. Substituting by total length is the reliable method.
Should I buy an extra ball?
Yes, it is good practice to buy one extra ball as a safety margin, especially for garments. Dye lots vary, and running out mid-project may mean a visible colour mismatch if the new ball comes from a different lot. This calculator rounds up to whole balls; add one more for security.
Does this account for gauge differences?
No. This calculator matches total yarn length only. Gauge (stitches and rows per 10 cm) affects how much yarn a project actually consumes and the finished dimensions. Always knit a tension swatch with your substitute yarn and adjust needle size to hit the pattern gauge before relying on the length estimate.
Sources and method
- Method: substitute by total length, computed as original ball count times length per ball, divided by the substitute's length per ball. All length figures are read by the user from each yarn's ball band.
- Unit conversion (yards to metres) per the National Institute of Standards and Technology: NIST unit conversion (1 yard = 0.9144 m exactly).
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.