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Textile & Yarn Converter

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Guide

Textile & Yarn Converter

Cross-reference knitting needle sizes, crochet hook sizes, and yarn weight categories across US, UK/Canada, metric, and Japanese standards in one place. Useful when a pattern from one country lists a needle or yarn name that does not match what is printed on your local supplies.

How to Use

Pick a category — Knitting Needle, Crochet Hook, or Yarn Weight.
Enter a size in the system you already know (millimeters, US number, UK number, Japanese, or US letter for hooks).
The matched row is highlighted in the reference table and the equivalents appear in the result card.
Use the quick-pick chips to jump to the most common sizes, or hit Print Reference Card to save the chart on paper.

Features

Four systems side-by-side — US, UK/Canada, metric (mm), and Japanese sizing on every row.
Knitting needles 2.0–25 mm — from sock-weight lace needles up to giant arm-knitting needles.
Crochet hooks B-1 through S — US letter/number labels, UK steel-hook numbers, and metric.
Yarn weight 0–7 — Craft Yarn Council categories with WPI (wraps per inch), gauge, and recommended needle/hook sizes.
Quick-pick chips — one click to load the most common sizes (DK, Worsted, 4 mm, H-8, etc.).
Print-ready — one click prints a clean reference card without the input form or site chrome.
No upload, no account — the lookup tables run entirely in your browser.

When You Need It

Following a UK pattern with US needles — UK numbering runs the opposite of US, so UK 7 is not US 7.
Substituting a “DK” yarn for “Light Worsted” or “8-ply” — same general category, different label by country.
Buying Japanese amigurumi supplies and matching them to US labels.
Identifying an unlabeled yarn by wrapping it around a ruler and counting WPI.
Picking the right needle size for a yarn you already own.

 FAQ

Why are US and UK knitting needle numbers reversed?

They evolved as two independent local industry conventions before any international standard existed. US sizing increases with needle diameter (bigger number = bigger needle), while UK/Canadian sizing was originally based on wire-gauge tables, which run the opposite way (bigger number = thinner wire). The metric system in millimeters sidesteps the problem by measuring the actual diameter directly.
What does WPI (wraps per inch) actually measure?

WPI is the number of times a single strand of yarn wraps snugly around a ruler over one inch, without overlapping or stretching. Because it captures the real diameter of the spun yarn, it is the most reliable way to identify an unlabeled yarn or compare two yarns from different brands. Roughly: 14+ WPI is fingering, 12 is sport, 11 is DK, 9 is worsted, 7 is bulky.
Why do Japanese needles have different sizes than US or metric?

Japanese needle sizing follows its own discrete steps (size 0 = 2.1 mm, size 15 = 6.6 mm) that do not align one-to-one with the US or metric system. The steps are smaller, so a Japanese pattern can specify a more precise needle than a US-only chart would offer. When converting, pick the nearest millimeter size unless the pattern specifies a particular gauge.
How are yarn weight categories standardized?

The Craft Yarn Council publishes a numbered system from 0 (Lace) to 7 (Jumbo) that most major US yarn brands use on their labels. The category groups several traditional names — for example, category 4 covers Worsted, Aran, and Afghan. Brands vary slightly within a category, so always knit a gauge swatch when substituting yarns.
Why is gauge more important than matching the needle size exactly?

Two knitters using the same yarn and the same labeled needle can produce different stitch counts per inch because of personal tension. Patterns are designed around a stitches-per-inch target, not the needle itself. If your gauge swatch is too tight, go up one needle size; if too loose, go down. The needle size on the label is a starting suggestion, not a rule.