Yarn Substitution Calculator
Match total length, not ball count.
Calculate how many balls of a substitute yarn a pattern needs, matching total yardage rather than ball count.
Balls to buy
13
to match 2200 yards
This is why substituting by ball count fails: buying the pattern's number of balls would leave you well short, discovered somewhere in the second sleeve. Match total length, never ball count.
How the Yarn Substitution Calculator works
The trap in substituting yarn is that balls are not a unit of anything. Two yarns of the same weight class and the same 100 gram ball can differ by 20% in length, so buying the same number of balls buys a different amount of yarn. Match the total yardage and the ball count falls out of it.
Also known as: yarn swap calculator · yarn replacement calculator
Why ball count is not a unit
Two yarns of the same weight class and the same 100 gram ball can differ by twenty percent or more in length, because length per gram depends on fibre density and how tightly the yarn is spun. A dense superwash merino and an airy woolen-spun at the same nominal weight are not the same amount of yarn.
So a pattern's ball count is only meaningful for the yarn the pattern used. Convert it to yardage first — balls times yards per ball — and then divide by your substitute's yardage per ball. That total yardage is the thing that has to match.
The error from skipping this step is always in the same direction when the substitute is shorter, and it is discovered late, because you knit the body and the first sleeve before the yarn runs out.
A worked example
A pattern calls for ten balls of a yarn at 220 yards each: 2,200 yards. Your substitute has 180 yards per ball. Two thousand two hundred divided by 180 is 12.2, so thirteen balls.
Buying ten balls instead — matching the pattern's ball count — would give 1,800 yards, leaving you 400 yards short. That is most of a sleeve, and by the time it becomes obvious the original dye lot is gone.
Where the answer misleads
Yardage tells you there is enough yarn. It does not tell you the substitution will work. Gauge is the first question: a yarn that cannot meet the pattern's gauge at a needle size you are happy with is the wrong yarn regardless of how much of it you buy.
Fibre behaviour is the second. A cotton substituted for wool at the same gauge hangs heavier and grows with wear; a superwash relaxes where a woolen-spun would bloom and fill in. The garment can be the right size on the needles and the wrong shape after a wash.
Swatch and block before buying the full quantity where the shop allows it. One ball is a cheap test against thirteen balls of a decision that cannot be undone.
Frequently asked questions
How do I substitute one yarn for another?
Multiply the pattern's ball count by the original yarn's yardage per ball to get total yardage, then divide by your substitute's yardage per ball and round up. Ten balls of 220 yards is 2,200 yards, which needs 13 balls of a 180 yard yarn.
What happens if I just buy the same number of balls?
You come up short by the difference. Ten balls of a 180 yard substitute against a 220 yard original is 400 yards missing — most of a sleeve, discovered at the worst possible moment.
Does the substitute need to be the same weight?
It needs to meet the pattern's gauge, which usually means the same weight class, but not always — a light worsted and a heavy DK overlap. Swatch before buying, because gauge decides whether the substitution works at all.
What else changes when I substitute?
Drape and fibre behaviour, which the yardage cannot tell you. A cotton substituted for a wool at the same gauge will hang heavier and grow more; a superwash will relax where a woolen-spun would bloom. Swatch and block before committing.