Understanding Yarn Weights (and Which Hook to Use)

By Double Crochet Editorial Team | Last Updated: November 2026

In crochet, yarn weight refers to the thickness (diameter) of the yarn strand—not how much the skein weighs in grams or ounces. The Craft Yarn Council (CYC) divides yarn into 8 standard categories numbered 0 (Lace, the thinnest) to 7 (Jumbo, the thickest), with each category paired to a standard crochet hook range—such as 4.5 mm–5.5 mm for #3 Light/DK and 5.5 mm–6.5 mm for #4 Medium/Worsted.

US vs. UK Terminology Note: While the 0–7 number symbols on yarn labels are universal, English-speaking countries use different words for the exact same yarn thicknesses: US Fingering (#1) is called 4-ply in the UK and Australia, US Light/DK (#3) is called 8-ply in Australia, and US Medium/Worsted (#4) overlaps with UK Aran and Australian 10-ply.

The Standard Yarn Weight Chart (#0 to #7)

Use this master reference chart to translate any yarn label's 0–7 category number into US trade names, UK and Australian ply names, Wraps Per Inch (WPI), typical meterage per 100 g skein, and the standard Craft Yarn Council crochet hook and gauge ranges:

\Note: Category #0 Lace gauge is measured in double crochet (dc) per 10 cm (4 in) by the Craft Yarn Council because lace thread is rarely worked in dense single crochet. To convert US hook letters to old UK numbers or Japanese sizes, see our complete hook size chart.*

US, UK, and Australian Yarn Names (The "Ply" Trap)

If you pick up a UK or Australian pattern that calls for "4-ply" or "8-ply" yarn, do not count the twisted strands inside your yarn!

• Why "Ply" means two different things:
  1. Structural plies (how a yarn is spun): A yarn spinner twists 2, 3, 4, or 8 individual strands ("plies") together to make a finished yarn of any thickness. A thick #5 Bulky yarn and a thin #1 Sock yarn can both be spun from 4 twisted strands.
  2. UK / Australian weight categories (historical naming): Decades ago, standard wool plies had a fixed thickness, so 4-ply meant a thin sock yarn and 8-ply meant a twice-as-thick double-knitting (DK) yarn. Today, UK and Australian labels still use 4-ply (#1), 8-ply (#3 DK), 10-ply (#4 Worsted/Aran), and 12-ply (#5 Bulky) strictly as thickness category names, regardless of how many strands are actually twisted together.

What Is the Difference Between DK, Worsted, and Aran Yarn?

Beginners are often surprised when two balls of yarn both marked #4 Medium feel noticeably different in thickness:

• #3 DK (Double Knitting / Light Worsted): Measures 11–15 WPI (~220–260 m per 100 g). Popular in UK/European patterns, baby garments, and lightweight granny squares; usually worked with a 4.0 mm (G-6) or 4.5 mm (7) hook.
• #4 Worsted (US Medium): Measures 10–12 WPI (~190–220 m per 100 g). The classic North American all-purpose weight for blankets, amigurumi, and scarves; usually worked with a 5.0 mm (H-8) or 5.5 mm (I-9) hook.
• #4 Aran (Heavy Worsted): Measures 8–10 WPI (~150–185 m per 100 g). Still labeled #4 Medium on the ball band, Aran is roughly 15–20% thicker than light worsted and is best worked with a 5.5 mm (I-9) or 6.0 mm (J-10) hook. Be careful when mixing a light #4 Worsted and a heavy #4 Aran in the same granny square blanket!

Which Hook to Use for Each Yarn Weight (Why Project Type Matters)

The hook size printed on a yarn label (and listed in the chart above) is a starting baseline for average flat fabric—not a rigid law. You should intentionally step up or down from the recommended hook range based on what you are making:

How to Identify an Unlabeled Mystery Yarn (WPI Method)

If you have a ball of stash yarn that lost its paper label, you can identify its exact 0–7 weight category in 60 seconds using Wraps Per Inch (WPI):

1. Wrap the yarn around a pencil or dowel rod: Take a standard wooden pencil, smooth pen barrel, or crochet hook handle and wrap the yarn around it for 3–5 cm (1.5–2 in).
2. Keep the wraps snug, not stretched: Lay each wrap right next to the previous wrap so there are no gaps between strands and no overlapping layers, without pulling the yarn so hard that its plies flatten out.
3. Count the wraps inside 1 inch (2.54 cm): Lay a ruler alongside the wrapped section and count how many individual strands sit inside a 1-inch window:
   • 14–30 wraps = #1 Super Fine (Fingering / 4-ply)
   • 12–18 wraps = #2 Fine (Sport)
   • 11–15 wraps = #3 Light (DK / 8-ply)
   • 9–12 wraps = #4 Medium (Worsted / Aran / 10-ply)
   • 6–9 wraps = #5 Bulky (Chunky / 12-ply)
   • 5–6 wraps = #6 Super Bulky
4. Plug your number into our calculator: Enter your wrap count (or weigh the remaining ball on a kitchen gram scale) in our wraps per inch calculator to get an instant weight match and starting hook recommendation.

Substituting Yarn Safely (Yardage & Meterage Math)

When a pattern calls for a discontinued or unavailable yarn, matching the #0–#7 category number is only Step 1. Because #4 Medium covers everything from light worsted (220 m/100 g) to heavy aran (150 m/100 g), always check two numbers on the label:

1. Match the meterage per 100 g within ±15%:
   • Worked Example: Suppose a sweater pattern uses 5 balls of a #4 Worsted yarn where each 100 g ball holds 200 m (219 yd).
   • Total length required: 5 balls × 200 m = 1,000 m (1,095 yd).
   • If you substitute a heavier #4 Aran yarn that only has 160 m per 100 g ball, buying 5 balls would give you only 5 × 160 m = 800 m—leaving you 200 m short!
   • Correct ball count: 1,000 m ÷ 160 m per ball = 6.25 balls → Buy 7 balls.
2. Match the fiber behavior: Substituting 100% cotton for 100% wool in the same #4 weight creates a heavier, less elastic fabric. Run your pattern's skein count and yardage through our yarn substitution calculator before buying.

Holding Two Strands Together (Doubling Yarn Weight)

What if your pattern calls for #5 Bulky or #4 Worsted yarn, and your stash is full of thinner #3 DK or #1 Fingering yarn? You can hold two strands together from two separate balls (or from the inside and outside of a center-pull cake) and crochet with them as if they were a single thick strand.

Because yarn thickness is based on cross-sectional area, holding two strands of #1 yarn does NOT equal #2—it jumps roughly 1 to 2 weight categories:

Remember the Double-Strand Yardage Rule: When you hold two strands together to make a project that requires 500 m of bulky yarn, you need 500 m of Strand A + 500 m of Strand B = 1,000 m total of the thinner yarn! Use our interactive holding yarn double calculator to combine any two or three yarn weights (even different weights like #4 Worsted + #1 Mohair) and calculate exact total yardage.

Frequently Asked Questions (FAQ)