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Unlocking the Mystery of Yarn Weights: Using Wraps Per Inch (WPI) to Identify Unknown Yarns

Unlocking the Mystery of Yarn Weights: Using Wraps Per Inch (WPI) to Identify Unknown Yarns

At Wild & Woolly Yarns, we know that discovering a beautiful skein of yarn without a label can be both exciting and a little daunting. How do you figure out the weight of the yarn to ensure it's suitable for your project? The answer lies in a handy technique called Wraps Per Inch (WPI). In this blog post, we'll delve into how WPI works, what it means, and how you can use it to determine the weight of unknown yarn.

What is Wraps Per Inch (WPI)?

Wraps Per Inch is a simple and effective method to measure the thickness of yarn. It involves wrapping the yarn around a ruler or another measuring device and counting how many times the yarn wraps around the tool within a one-inch span. This number helps to classify the yarn into standard weight categories, such as lace, fingering, sport, DK, worsted, bulky, and super bulky.

How to Measure WPI: Step-by-Step Guide

  1. Gather Your Materials: You’ll need a ruler and the yarn you want to measure.

  2. Wrap the Yarn: Hold the end of the yarn against the ruler at the 0-inch mark. Begin wrapping the yarn around the ruler, keeping the wraps close together but not overlapping. Continue until you have covered one inch.

  3. Count the Wraps: Count the number of times the yarn wraps around the ruler within that one-inch span. Be sure to count accurately, as this number is crucial for determining the yarn weight.

  4. Refer to the WPI Chart: Use the WPI chart below to determine the weight category of your yarn based on the number of wraps per inch.

WPI Chart:

  • Lace: 18+ WPI
  • Fingering/Sock: 14-17 WPI
  • Sport: 12-14 WPI
  • DK: 11-13 WPI
  • Worsted: 9-11 WPI
  • Aran: 8-10 WPI
  • Bulky: 7-9 WPI
  • Super Bulky: 5-6 WPI

What Does WPI Mean?

The WPI measurement gives you a good indication of the yarn's thickness, which corresponds to its weight category. This is essential for matching the yarn to appropriate knitting or crochet patterns, ensuring your finished project has the correct gauge and drape.

Using WPI to Identify Yarn Weight:

  • Gauge Consistency: Once you know the WPI of your yarn, you can compare it to the recommended yarn weights in your pattern. This helps ensure that your project will turn out as intended.

  • Substitution Made Easy: If you have a pattern that calls for a specific yarn weight but want to use your mystery yarn, knowing its WPI allows you to substitute confidently, adjusting the needle size and gauge as necessary.

  • Project Planning: Understanding the weight of your yarn is crucial for planning your projects. It helps in determining how much yarn you'll need and what type of projects the yarn is best suited for.

Tips and Tricks:

  • Consistency is Key: When wrapping the yarn, maintain consistent tension to get an accurate WPI measurement.

  • Double-Check: Measure the WPI in a few different places along the yarn to ensure accuracy, as yarn thickness can sometimes vary slightly.

  • Keep a WPI Tool Handy: Investing in a dedicated WPI tool can make the process quicker and easier, providing you with accurate measurements every time.


Using Wraps Per Inch (WPI) is a straightforward and reliable method to identify the weight of unknown yarns. By mastering this technique, you can confidently incorporate unlabelled or mystery yarns into your knitting and crochet projects, ensuring they turn out beautifully. At Wild & Woolly Yarns, we're always here to help you with any questions you have about yarn weights, WPI, or any other knitting and crochet needs.

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