How to use the yarn substitution calculator
- Find the pattern yarn's length and weight per ball. Patterns usually print them; if not, look up the yarn on the maker's site.
- Enter how many balls the pattern asks for in your size.
- Enter the length and weight per ball of the yarn you want to use, from its label.
- Add a price per ball if you want a total cost.
- Read the thickness check, then knit a swatch before you buy the full amount.
How yarn substitution works
A pattern uses a certain length of yarn. Weight only matters because labels sell yarn by the ball, and balls of different yarns hold different lengths. So the calculator turns the pattern's balls into yards, then counts how many of your balls cover that length.
The second check compares the two yarns by length per 100 grams. If your yarn has noticeably fewer yards in the same weight, it is probably thicker or made of a heavier fiber. It may not knit to the pattern gauge on the same needle. When the gap is over the threshold the result is marked in red and suggests a swatch. A small gap is no guarantee either, since twist and fiber change how yarn knits up.
Formulas
- Total yards = pattern yards per ball × balls called for.
- Your balls = total yards ÷ your yards per ball, rounded up.
- Yards per 100 g = yards per ball × 100 ÷ grams per ball.
- Difference = (yours − pattern) ÷ pattern × 100%.
- Cost = your balls × price per ball.
Worked example: swapping a worsted
The pattern calls for 5 balls of a yarn with 220 yards in 100 grams: 5 × 220 = 1,100 yards. Your yarn has 105 yards in a 50 gram ball, so 1,100 ÷ 105 = 10.5, rounded up to 11 balls. You buy 1,155 yards and have 55 to spare.
For the check, the pattern yarn has 220 yards per 100 g and yours has 105 × 100 ÷ 50 = 210. That is 4.5 percent less, inside the 10 percent guideline. Had you picked a yarn with 137 yards per 50 grams, it would be 274 yards per 100 g, 24.5 percent more than the pattern yarn. The calculator would then ask you to swatch, because it is likely a thinner yarn.
Balls needed for 1,100 yards
Common ball sizes, with the thickness check against a 220 yards per 100 g pattern yarn.
| Your ball | Balls | Yd per 100 g | Check |
|---|---|---|---|
| 100 yd / 50 g | 11 | 200 | Similar |
| 110 yd / 50 g | 10 | 220 | Similar |
| 125 yd / 50 g | 9 | 250 | Swatch first |
| 137 yd / 50 g | 9 | 274 | Swatch first |
| 190 yd / 100 g | 6 | 190 | Swatch first |
| 220 yd / 100 g | 5 | 220 | Similar |
| 250 yd / 100 g | 5 | 250 | Swatch first |
How much extra to buy
Sources suggest different safety margins. Lion Brand works through the same method as this calculator and then says it is wise to buy one extra ball. Love Life Yarn suggests 10 to 15 percent extra, or one safety skein, to cover swatching and finishing. Here is what each choice means for the worked example above.
| Margin | Balls | Spare yards |
|---|---|---|
| None, exact | 10.5 | 0 |
| Rounded up (the calculator) | 11 | 55 |
| Rounded up plus one ball (Lion Brand) | 12 | 160 |
| 10% extra (Love Life Yarn) | 12 | 160 |
| 15% extra (Love Life Yarn) | 13 | 265 |
To add a percentage yourself, raise the pattern's yards per ball by that much before you enter it. Rounding up already leaves 55 yards spare here, so the extra ball matters most when your gauge is looser than the pattern's or you plan to make the piece longer. Lion Brand also asks you to check both the color number and the dye lot, since batches can differ in color.
Holding two strands together
Two strands of a thin yarn held together act like one thicker yarn. Sources disagree on how much thicker. Love Life Yarn lists two strands of fingering as close to DK, two of sport as close to worsted and two of worsted as close to bulky. FiberGypsy says two strands of fingering can replace one strand of worsted. It suggests multiplying the single-strand gauge by about 0.72, so a fingering yarn at 28 stitches per 4 inches gives roughly 20 held double. Only a swatch settles it.
For the yardage, remember that every stitch uses both strands. Enter half the yards per ball of your yarn. A fingering yarn with 400 yards in 100 grams then counts as 200 yards per ball, and the 1,100 yard pattern needs 6 balls. The thickness check compares 200 with 220 yards per 100 g, 9.1 percent apart, which hints that the doubled strand is close to the pattern yarn's thickness.
Finding a substitute yarn
This calculator checks a yarn you have already picked. To find candidates, look for yarns with the same weight, gauge and fiber as the original, for example on Ravelry or the yarn maker's site. The guide to substituting yarn covers the rest of the choice, from fiber to swatching, and the yarn yardage converter turns grams, yards and meters into each other for a single yarn.
Tips for substituting yarn
- Match the fiber when you can. A cotton swapped for a wool of the same length per weight will still drape and stretch differently.
- Buy all your balls from one dye lot. Colors can shift between lots, and it shows across a sweater.
- Swatch in the new yarn, wash the swatch and measure it before casting on.
- If the yarn is a different thickness and you like the fabric, use our gauge calculator to rework the stitch counts.
- Keep the ball band. It has the yardage, dye lot and care instructions in one place.
