WPI (Wraps Per Inch)
WPI (Wraps Per Inch) is a simple method for measuring yarn weight by wrapping yarn around a ruler and counting the number of wraps in one inch.
Explanation
WPI is a practical method for finding out which weight category an unknown yarn belongs to. You wrap the yarn closely, but without stretching it, around a ruler or a needle over one inch (2.54 cm). By counting the number of wraps, you can determine if the yarn is fingering, DK, worsted, or another thickness. This is especially useful for yarn without a label or if you want to use leftover yarn and are unsure of its thickness.
Also known as: Wraps per inch
How to measure
Wind the yarn around a ruler or a pencil over one inch, laying the wraps snugly side by side with no gaps and no stretching. The number of wraps is the yarn’s WPI.
It is a direct measurement of thickness, independent of what the manufacturer chose to call the yarn. That makes WPI especially useful for yarn without a ball band, handspun, and leftovers of unknown origin.
Approximate values
Around 30 to 40 wraps or more is lace, 18 to 22 is fingering, 14 to 18 is sport, 12 to 15 is DK, 9 to 12 is worsted and 6 to 9 is bulky. The boundaries are soft and overlapping, so treat the number as an indication and confirm with a swatch.
Common mistakes
- Wrapping too tightly, compressing the yarn and inflating the WPI.
- Measuring yarn already stretched from a ripped-out project.
Keywords
- wpi
- wraps per inch
- yarn weight
- measure yarn
Frequently asked questions
What is WPI used for?
Working out the weight of yarn you cannot identify: handspun, band-less leftovers, or yarn with unfamiliar labeling.
Is WPI more accurate than the weight category?
It measures thickness directly, whereas the category is the manufacturer’s judgement. But neither replaces a swatch.