Wraps Per Inch (WPI) Calculator
Wind the yarn side by side along a ruler until an inch is full: that count is the WPI, and it maps onto the standard weight numbers. It is how you classify a yarn with no band, or a leftover — around 12 WPI is usually worsted.
Your numbers
Yarn weight number
4
Stitches per 10 cm
23sts/10 cm
Formula
Stitches per 10 cm ≈ Wraps per inch × 1.9
Winding under tension raises the WPI and makes the yarn read thinner than it is. Lay the wraps together without squashing them.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Wraps per inchWraps filling one inch on a ruler; winding tight inflates it. | 12 | 3 ~ 40 |
Step by step
Quick reference table
Results when only Wraps per inch changes and everything else stays put.
| Wraps per inch | Yarn weight number | Stitches per 10 cm (sts/10 cm) |
|---|---|---|
| 6 | 6 | 11 |
| 9 | 5 | 17 |
| 12 | 4 | 23 |
| 18 | 1 | 34 |
| 24 | 1 | 46 |
What each result means
| Result | At default values |
|---|---|
| Yarn weight numberYarn weight number — 0 is lace, 6 is super bulky. | 4 |
| Stitches per 10 cm (sts/10 cm)Stitches in 10 cm. If you measured over 5 cm, double it before entering. | 23 |
Common mistakes
Winding under tension raises the WPI and makes the yarn read thinner than it is. Lay the wraps together without squashing them.
Glossary
- Wraps per inch
- Wraps filling one inch on a ruler; winding tight inflates it.
- Yarn weight number
- Yarn weight number — 0 is lace, 6 is super bulky.
- Stitches per 10 cm
- Stitches in 10 cm. If you measured over 5 cm, double it before entering.
Frequently asked questions
Q. How is Wraps Per Inch (WPI) Calculator calculated?
Stitches per 10 cm ≈ Wraps per inch × 1.9 — Wind the yarn side by side along a ruler until an inch is full: that count is the WPI, and it maps onto the standard weight numbers. It is how you classify a yarn with no band, or a leftover — around 12 WPI is usually worsted.
Q. Can you walk through an example?
With Wraps per inch 12, the answer is Yarn weight number 4.
Q. What do I need to enter?
Enter Wraps per inch. 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 Wraps per inch moves the answer to Wraps per inch 6 → Yarn weight number 6 and Wraps per inch 24 → Yarn weight number 1. 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?
Winding under tension raises the WPI and makes the yarn read thinner than it is. Lay the wraps together without squashing them.
Related calculators
Materials differ in density and absorption. If your label states a figure, use it — the defaults here are only common values.