Crochet Hook Size Chart: US, UK and Metric

Why Crochet Hook Sizes Look Different

Crochet hooks can use metric measurements, US letters and numbers, or older UK numbers. The same hook may therefore have more than one label. Metric sizing is the clearest system because the number gives the hook diameter in millimeters.

Crochet Hook Size Conversion Chart

Use these common conversions as a quick reference:

• 2.25 mm = US B-1 = UK 13
• 2.75 mm = US C-2 = UK 12
• 3.25 mm = US D-3 = UK 10
• 3.75 mm = US F-5 = UK 9
• 4 mm = US G-6 = UK 8
• 4.5 mm = US 7 = UK 7
• 5 mm = US H-8 = UK 6
• 5.5 mm = US I-9 = UK 5
• 6 mm = US J-10 = UK 4
• 6.5 mm = US K-10.5 = UK 3
• 7 mm = UK 2
• 8 mm = US L-11 = UK 0
• 9 mm = US M/N-13 = UK 00
• 10 mm = US N/P-15 = UK 000

Some sizes do not have a direct US or old UK label, so use the metric measurement when possible.

Why Metric Size Is Useful

US hook letters and numbers are not based on one universal measurement system. Manufacturers can sometimes label similar hooks differently.

Metric size gives you the actual diameter, making it the safest value to compare.

Hook Size and Gauge

A hook conversion tells you which physical hook is closest, but it does not guarantee the correct fabric.

Your tension, yarn, stitch pattern, and hook material can all affect gauge.

If your swatch is larger than the pattern gauge, try a smaller hook. If your swatch is smaller, try a larger hook, then measure again.

Use the Gauge Calculator

After choosing your hook, make a swatch and enter your stitch measurement in the Gauge Calculator.

Compare the result with the pattern gauge before starting the full project.

Before You Start

Treat this chart as a conversion reference, not a replacement for swatching.

Check the millimeter marking printed on your hook whenever possible, especially when using older hooks or hooks from different manufacturers.