Yarn Substitution Calculator
What you match when swapping yarn is length, not weight. A pattern calling for eight 50 g balls of a yarn that runs 400 m per 100 g wants 1,600 m. A substitute at 320 m per 100 g carries only 160 m per ball, so you need ten — buy the same eight and you are 320 m short.
Your numbers
Balls
10balls
Yarn length needed
1,600m
Formula
Balls = ⌈Balls the pattern calls for × Original yarn, m per 100 g ÷ Substitute yarn, m per 100 g⌉
Matching length does not match thickness. Two yarns with the same metres per 100 g can drape and stretch quite differently once one is alpaca and the other cotton, so swatch the substitute before committing. If it is sold in a different ball size, divide the total metres above by that label instead.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Original yarn, m per 100 g (m)The pattern yarn's label length scaled to 100 g — 200 m per 50 g is 400. | 400 | 1 and up |
| Substitute yarn, m per 100 g (m)The same figure for the yarn you are swapping in; this is what you match, not the weight. | 320 | 1 and up |
| Balls the pattern calls for (balls)Balls the pattern lists for your size — read the row for your size, not the first one. | 8 | 1 and up |
| Grams per ball (g)Grams in one ball — usually 50 or 100. | 50 | 1 and up |
Step by step
Quick reference table
Results when only Original yarn, m per 100 g (m) changes and everything else stays put.
| Original yarn, m per 100 g (m) | Balls (balls) | Yarn length needed (m) |
|---|---|---|
| 200 | 5 | 800 |
| 300 | 8 | 1,200 |
| 400 | 10 | 1,600 |
| 600 | 15 | 2,400 |
| 800 | 20 | 3,200 |
What each result means
| Result | At default values |
|---|---|
| Balls (balls)Balls to buy; you cannot split one, so it rounds up. | 10 |
| Yarn length needed (m)The yarn length in metres, matching the label. | 1,600 |
Common mistakes
Matching length does not match thickness. Two yarns with the same metres per 100 g can drape and stretch quite differently once one is alpaca and the other cotton, so swatch the substitute before committing. If it is sold in a different ball size, divide the total metres above by that label instead.
Glossary
- Original yarn, m per 100 g
- The pattern yarn's label length scaled to 100 g — 200 m per 50 g is 400.
- Substitute yarn, m per 100 g
- The same figure for the yarn you are swapping in; this is what you match, not the weight.
- Balls the pattern calls for
- Balls the pattern lists for your size — read the row for your size, not the first one.
- Grams per ball
- Grams in one ball — usually 50 or 100.
- Balls
- Balls to buy; you cannot split one, so it rounds up.
- Yarn length needed
- The yarn length in metres, matching the label.
Frequently asked questions
Q. How is Yarn Substitution Calculator calculated?
Balls = ⌈Balls the pattern calls for × Original yarn, m per 100 g ÷ Substitute yarn, m per 100 g⌉ — What you match when swapping yarn is length, not weight. A pattern calling for eight 50 g balls of a yarn that runs 400 m per 100 g wants 1,600 m. A substitute at 320 m per 100 g carries only 160 m per ball, so you need ten — buy the same eight and you are 320 m short.
Q. Can you walk through an example?
With Original yarn, m per 100 g 400m, Substitute yarn, m per 100 g 320m, Balls the pattern calls for 8balls, Grams per ball 50g, the answer is Balls 10balls.
Q. What do I need to enter?
Enter Original yarn, m per 100 g, Substitute yarn, m per 100 g, Balls the pattern calls for, Grams per ball. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Original yarn, m per 100 g (m) moves the answer to Original yarn, m per 100 g (m) 200 → Balls (balls) 5 and Original yarn, m per 100 g (m) 800 → Balls (balls) 20. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Matching length does not match thickness. Two yarns with the same metres per 100 g can drape and stretch quite differently once one is alpaca and the other cotton, so swatch the substitute before committing. If it is sold in a different ball size, divide the total metres above by that label instead.
Related calculators
Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.