Why Needle Sizes Are Confusing
Knitting needle and crochet hook sizing is confusing because four different systems exist simultaneously: US sizes (numbers and letters), metric (millimeters), UK sizes (numbers that run backwards compared to US), and Japanese sizes (their own numbering system).
The US system is the most common in North American patterns. Metric is universal and used in most modern patterns worldwide. UK sizes are found in older British patterns and some Australian ones. Japanese sizes appear in Japanese knitting books, which have become popular globally.
The core problem is that US and UK numbering goes in opposite directions. US 14 is a large needle (10.0mm) while UK 14 is a tiny needle (2.0mm). Mix these up and your project will be wildly wrong.
Knitting Needle Size Reference
Here are the most commonly used sizes:
For lace and fingering weight yarn: US 0–3 (2.0–3.25mm). These tiny needles create the fine gauge needed for socks, shawls, and delicate garments.
For sport and DK weight: US 3–7 (3.25–4.5mm). The sweet spot for lightweight garments, baby items, and accessories.
For worsted and aran weight: US 7–9 (4.5–5.5mm). The most popular range. This is where most beginners start.
For bulky weight: US 10–11 (6.0–8.0mm). Great for quick projects like chunky scarves and blankets.
For super bulky and jumbo: US 13–50 (9.0–25.0mm). These oversized needles are used for arm knitting and extreme chunky projects.
Crochet Hook Sizing
Crochet hooks use letter sizes in the US (B through S) alongside millimeter sizes. The letter system only covers hooks from 2.25mm to 15.75mm, so very small and very large hooks are referenced only by millimeter size.
Steel crochet hooks (used for thread crochet and lace) have their own separate numbering system where the numbers go in the opposite direction: steel size 14 is the smallest (0.75mm) and steel size 00 is the largest (3.5mm).
The most commonly used crochet hooks are H/8 (5.0mm) for worsted weight and I/9 (5.5mm) for slightly looser worsted. These two hooks cover the majority of crochet patterns.
When to Go Up or Down a Size
If your gauge swatch has too many stitches per inch, your tension is tight — go up one needle size. If your swatch has too few stitches per inch, your tension is loose — go down one size.
Some crafters consistently knit tight and always need to go up a size from the pattern recommendation. Others consistently knit loose. Learning your personal tendency saves time on future projects.
Use our Needle and Hook Size Converter to instantly see any size across all four systems, so you can confidently work from patterns written in any country's notation.