Wraps Per Inch (WPI) Method
Wraps per inch is a way of measuring yarn weight by wrapping the yarn snugly around a ruler and counting how many wraps fit in one inch. It is more reliable than the ball-band weight category for comparing unknown yarns.
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Method
Wrap the yarn around a smooth ruler or pencil with a 1-inch gap marked. Wraps should sit side-by-side without gaps and without compressing. Count the number of wraps that fit in one inch.
Reading the result
6–8 wpi: super bulky. 9–11 wpi: bulky. 12–14 wpi: worsted/aran. 14–18 wpi: DK/light worsted. 18–22 wpi: sport. 22–28 wpi: fingering/sock. 28+: lace.
In partnership Tools and supplies that make this technique easier.
When to use
When yarn comes off the ball band or out of a stash with unknown weight. When comparing two yarns with similar but not identical labels. When verifying a yarn substitution before swatching.
Limitations
WPI is a guide, not a guarantee — yarns of the same wpi can knit up at different gauges depending on fibre and ply structure. Always swatch as the final test.
Abbreviation reference
| Abbreviation | Meaning |
|---|---|
| WPI | wraps per inch |
| CYC | Craft Yarn Council |
Tips
- Wrap snugly but do not compress the yarn — both extremes throw off the count.
- Use a smooth ruler or wooden pencil for the most accurate count.
- WPI is most useful for unlabelled yarn from a stash or destash.
In depth
Wraps per inch quantifies the diameter of the yarn directly, which is closely correlated with the gauge the yarn will produce. Because WPI measures the yarn itself rather than relying on a label, it is the most reliable way to compare two yarns of unknown or different brands.