Understanding Yarn Weights: How to Determine Yarn Weight Using Wraps Per Inch (WPI)

Understanding yarn weights is important for choosing the right type of yarn for a project. Let me tell you a story about how I learned about yarn weights. When I first got back into crocheting, I decided to make the Driftwood Poncho by Mama in a Stitch. It's a beautiful pattern that calls for Lion Brand’s Scarfie yarn, which is a bulky weight (5) yarn. But instead of waiting to get the right yarn, I used a worsted weight (4) yarn I already had. As I got halfway through the pattern, I realized my poncho was turning out way too small—definitely not what I wanted!

This story teaches us two important lessons. First, it's crucial to always make a gauge swatch. And second, it's important to recognize that yarn comes in different weights. Alright, let's dive in! But before we start, don't forget to save this tutorial for later by pinning it!

Just a heads-up: This blog post may contain affiliate links. Don't worry, though - these links are a win-win! They help support our site without costing you a penny extra. So, if you find something you love, clicking through won't just benefit us, but it'll also help you discover great products and resources!

Yarn Weights Chart

There are eight thickness levels of yarn, labeled with numbers 0 to 7:

Video Tutorial

I have a video tutorial that demonstrates how to measure wraps per inch, or WPI to determine a yarn’s weight.

What Yarn Weight Should I use for my Project?

1. Lace (0): This is the finest weight of yarn available. It is often used for delicate projects like shawls, doilies, and fine garments. Lace weight yarn produces lightweight and airy fabrics with intricate stitch definition.

2. Super Fine (1): Also known as fingering or sock weight yarn, super fine yarn is slightly heavier than lace weight. It is commonly used for making socks, lightweight garments, and intricate lace patterns. Super fine yarn creates delicate and drapey fabrics.

3. Baby (2): Fine weight yarn is slightly heavier than super fine yarn but still produces lightweight fabrics. It is suitable for making baby garments, shawls, and lightweight accessories. Fine yarn often results in soft and breathable fabrics.

4. DK (3): Light weight yarn, also known as DK (double knitting) weight, is a versatile yarn suitable for a wide range of projects. It is commonly used for making sweaters, scarves, hats, and blankets. Light weight yarn produces fabrics that are warm yet not too bulky.

5. Worsted (4): Also known as worsted or Aran weight yarn, medium weight yarn is one of the most popular yarn weights. It is suitable for a variety of projects, including garments, accessories, and home decor items. Medium weight yarn produces sturdy and durable fabrics with good stitch definition.

6. Bulky (5): Bulky weight yarn is thicker and heavier than medium weight yarn. It is ideal for making quick projects like hats, scarves, and blankets. Bulky yarn creates warm and cozy fabrics with a plush texture.

7. Super Bulky (6): Super bulky weight yarn is even thicker and heavier than bulky weight yarn. It is perfect for making chunky accessories and home decor items. Super bulky yarn produces thick and warm fabrics with a bold and modern look.

8. Jumbo (7): Jumbo weight yarn is the thickest and heaviest yarn available. It is used for making large-scale projects like blankets, rugs, and oversized garments. Jumbo yarn creates thick and lofty fabrics with a luxurious feel.

What is Yarn Ply?

You may have encountered the term "ply" in yarn descriptions, like single-ply, 2-ply, 3-ply, and so on. Ply refers to the number of individual strands twisted together to form a single yarn strand. Generally, single-ply yarn is lighter than 2-ply, which is lighter than 3-ply, and so forth, but this isn't always the case.

Yarn ply can impact a yarn’s characteristics, such as thickness, strength, and texture. Multiple plies typically result in stronger and more durable yarn, while single-ply yarns tend to be softer and more delicate. Understanding ply is important for choosing yarn, as it can affect how a project drapes, its stitch definition, and its overall appearance. Additionally, ply influences a yarn's resilience to wear and tear, making it a consideration for projects subject to heavy use.

While understanding yarn ply is crucial, it doesn't fully indicate the yarn's weight. Although ply can influence strength and texture, it doesn't directly correspond with weight or thickness. For example, a 2-ply yarn consists of two strands twisted together, but each strand could vary in weight from lace to worsted. Ply is just one factor to consider when selecting yarn, and while you may encounter it in yarn descriptions, remember it's not a measure of weight or thickness.

Why Are There So Many Different Names for Yarn Weights?

The varying names for yarn weights can be attributed to several factors:

1. Historical Evolution: Over time, yarn weights have evolved, and different terms have been used to describe them. For example, terms like "lace," "fingering," and "worsted" have historical origins related to the types of projects or garments they were traditionally used for.

2. Regional Preferences: Different regions or countries may have their own naming conventions for yarn weights based on popular usage or industry standards. For instance, terms like "DK" (double knitting) or "Aran" are more commonly used in certain regions like the UK, while terms like "worsted" or "sport" may be more prevalent in the US.

3. Manufacturer Branding: Yarn manufacturers may also introduce their own branded names for yarn weights to differentiate their products in the market. These names may reflect specific characteristics of the yarn or be part of a marketing strategy to appeal to consumers.

4. Ease of Understanding: Some yarn weight names are chosen to make it easier for crafters to understand the thickness and suitability of the yarn for their projects. For example, terms like "super bulky" or "lace" provide clear indications of the yarn's weight and intended use.

Due to the variations in naming conventions for yarn weights, using the number system or wraps per inch (WPI) provides a clear and straightforward way to understand yarn weights without any confusion.

Determining Yarn Weights With Wraps per Inch (WPI)

As mentioned, yarn weight is determined by its thickness, or diameter. But how do you measure the diameter of a single strand of yarn? By using a measurement technique called wraps per inch or WPI. You can find out WPI by following these steps:

1. Prepare Your Yarn: Take a strand of yarn that you want to measure. Make sure it's untangled and smooth.

2. Wrap Around Ruler: Take the yarn and loosely, yet snugly, wrap it around a ruler or any object with a known width, like a pencil. Be sure not to stretch the yarn while wrapping.

3. Count Wraps: Count the number of times the yarn wraps around the ruler in one inch. Make sure the wraps are snug but not overlapping.

4. Calculate WPI: The count of wraps you get is your wraps per inch (WPI).

Alternatively, you can use a WPI tool (this one from Knit Picks is my favorite).

Measuring yarn weight with WPI becomes valuable when you don't have the label for a skein of yarn or are gifted yarn without labels.

What Size Crochet Hook Should I Use With Each Yarn Weight?

Each yarn weight category has a range of recommended hook sizes. When substituting a different yarn weight, you'll probably need to adjust the hook size from what's specified in the pattern. Here is a rough guideline of what hook sizes are typically recommended for each yarn weight:

1. Lace (0): Recommended hook size: 2.25mm (B-1) to 3.5mm (E-4)

2. Super Fine (1): Recommended hook size: 3.5mm (E-4) to 4.5mm (7)

3. Baby (2): Recommended hook size: 4.5mm (7) to 5.5mm (I-9)

4. DK (3): Recommended hook size: 5.5mm (I-9) to 6.5mm (K-10.5)

5. Worsted (4): Recommended hook size: 6.5mm (K-10.5) to 9mm (M-13)

6. Bulky (5): Recommended hook size: 9mm (M-13) to 16mm (Q)

7. Super Bulky (6): Recommended hook size: 16mm (Q) and larger

8. Jumbo (7): Recommended hook size: 11.5mm (P-16) and larger

How Do I Substitute Yarn Weights?

Substituting yarn weights in patterns can open up a world of possibilities. Maybe you have a favorite pattern, but you want to use a different weight yarn than what's specified. Understanding how to make these substitutions can help you customize projects to your liking and make the most of your yarn stash.

Here are some tips for successfully substituting yarn weights:

1. Consider Yarn Characteristics: Take into account the characteristics of the yarn you're substituting. Is it similar in texture, fiber content, and drape to the yarn called for in the pattern? Choosing a substitute yarn with similar qualities can help ensure a successful outcome.

2. Adjust Hook or Needle Size: When substituting yarn weights, you will likely need to adjust your hook size to achieve the correct gauge. A thicker yarn will typically require a larger hook size, while a thinner yarn may need a smaller size. Make a gauge swatch with your chosen yarn and adjust your hook size as needed to match the pattern's gauge.

3. Calculate Yardage: Keep in mind that yarn weight substitutions can affect the yardage required for a project. Thicker yarns generally cover more surface area than thinner yarns, so you may need less yardage when using a heavier-weight yarn. Conversely, thinner yarns may require more yardage to achieve the same-size project.

4. Test Before Committing: Before diving into your project, make a small swatch with your chosen substitute yarn to test how it works up with the pattern stitch. This will give you a chance to assess the fabric's drape, texture, and overall appearance before committing to the entire project.

With these tips in mind, you can confidently substitute yarn weights in your favorite patterns and create beautiful projects that reflect your unique style and creativity.