Wraps Per Inch

WPI or Wraps per Inch refers to the way in which the weight of your yarn is determined. 

Yarn weight can be a very fluid concept: it can differ depending on your location; and just like clothing sizes, it can vary greatly from vendor to vendor.  Wraps per inch is the great equalizer.  It literally refers to how many times your yarn can be wrapped around a ruler within the space of 1 inch, thus limiting the amount of interpretation involved when it comes to the weight of your yarn.

This is the chart that I use to determine yarn weight, and also what craft tools (in US sizes) we recommend with each weight of yarn:

Yarn Weight  Wraps Per Inch  Knitting Needle Size   Crochet Hook Size
Bulky          4 - 6             8 - 12      L-11 or M/N 13
Aran          7 - 8             6 - 10      J-10 or K-10.5
Worsted          9 - 11              5 - 8          H-8 or I-9
Dk          11 - 13              4 - 7            G-6 or 7
Sport          14 - 17              2 - 5          E-4 or F-5
Fingering          18 - 21              1 - 4          C-2 or D-3
Lace          22 - 28              0 - 3     Steel hook or B-1


These sizes are a recommendation.  Each person crafts a little differently: always use the size of needle/hook that achieves the correct swatch gauge specified in your pattern.

If you'd like to know more about how to determine your yarn's weight using the WPI method, check out my Yarn Weight Tutorial.


If you still have questions, please Contact Us - We'd love to hear from you!