Skeins for a yarn swap
How many balls of my yarn do I buy?
Knitting a pattern in a different yarn? Enter what the pattern needs and the length of one ball of yours.
Worked example
A pattern that needs 1,200 yd, in a yarn with 200 yd per ball: buy 7 balls (6 without the 10% margin).
How it works
Everything is worked out in meters (a yard is 0.9144 m), then divided by the length of one of your balls and rounded up: you can't buy part of a ball.
The safety margin covers a slightly different gauge, a swatch, and dye lots — running out and finding the same dye lot later is often impossible. 10% is a sensible default; go higher for a pattern with big texture or if you're lengthening anything.
Swap only between yarns of the same weight. Tick the check and fill in the length and grams from both labels, and the calculator compares their length per 100 g: within 10% of each other is close enough to swap, the same rule Yarn substitutes uses.
A pattern that gives grams ("400 g of DK") is turned into length with its yarn's label: the grams times that yarn's length per gram.
With several colors, each one is worked out and rounded up on its own: you can't share a ball between two colors, so the total can be a ball or two more than one color would need.
Balls you already have come off what you buy. Add the price of one ball, and you see what the rest will cost.
Pick a yarn by name and its label fills in: from your stash first, then the yarn catalog. Check the numbers against your own label: some yarns come in more than one ball size.