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Understanding Wraps Per Inch (WPI) and its Practical Applications

Pink yarn, unravelled ready to measure wraps per inch

Choosing the right yarn for your knitting or crochet projects can be a daunting task, especially with the wide array of options available. Among the various ways to determine the thickness and suitability of a yarn, WPI (Wraps Per Inch) is a valuable tool that allows yarn enthusiasts to gauge yarn thickness and make informed decisions for their projects.

What is WPI (Wraps Per Inch)?

WPI, or Wraps Per Inch, is a simple and effective method of measuring the thickness or "weight" of a yarn. It involves wrapping the yarn around a standardised object, such as a ruler or a WPI tool specifically designed for this purpose, and then counting the number of wraps made in one inch. The WPI value helps identify the yarn's thickness and can be compared to industry standards to determine its yarn weight category.

How to Measure WPI:

Measuring the WPI of a yarn is a straightforward process. Follow these steps:

  1. Prepare a WPI tool or a ruler with clearly marked inches.

  2. Choose a section of the yarn you want to measure, ensuring it is untwisted and consistent in thickness.

  3. Start wrapping the yarn around the tool or ruler, aligning the wraps neatly side by side.

  4. Count the number of wraps made in one inch. The total wraps will represent the WPI of the yarn.

Interpreting WPI and Selecting Yarn for Projects:

Now that we understand how to measure WPI, let's explore how it can assist in selecting the appropriate yarn for specific projects.

  1. Matching Yarn Weight: WPI helps match the yarn to a particular yarn weight category, such as cobweb lace (1ply), lace (2ply), fingering (4ply), sport (5ply), DK (8ply), worsted (10ply) or bulky (12ply). Industry standards exist for these categories, making it easier to determine if a yarn is suitable for your project. For instance, if the WPI falls within the range of 18-20, it's likely a fingering weight yarn.

  2. Substituting Yarns: WPI can be a valuable tool when substituting yarns in patterns. If you don't have the recommended yarn for a project, you can use WPI to find a suitable replacement that matches the required yarn weight.

  3. Achieving Consistency: When working on a project that requires multiple skeins of yarn, using WPI can help ensure consistency across all skeins. This is crucial to maintain an even texture and appearance throughout your project.

WPI vs. Yarn Weight and Meterage:

While WPI is a useful tool, it's essential to consider it alongside other factors like yarn weight and meterage. Each method provides different insights that collectively aid in making informed decisions:

  1. Yarn Weight: Yarn weight categorisations (lace, fingering, etc.) are standardised and help you quickly identify the thickness of a yarn. It can give a general idea of the yarn's characteristics and its recommended use.

  2. Meterage/Yardage: Knowing the total length of yarn in a skein (meterage or yardage) is crucial for estimating how much yarn you'll need for your project. This information ensures you purchase the right amount and avoid running out mid-project.


Wraps Per Inch (WPI) is a valuable tool that allows yarn enthusiasts to determine the thickness of a yarn and its weight category. By measuring the WPI and comparing it to industry standards, crafters can select the perfect yarn for their projects or confidently substitute yarns when needed. While WPI is a helpful method, it's even more effective when combined with other factors like yarn weight and meterage. Understanding these yarn characteristics empowers crafters to create stunning and consistent projects with the ideal yarn choice.

Looking for the perfect yarn for your next project? Check out our range of yarns in our online store!


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