Crochet Hook Size Converter

Three ways to name the same hook

Crochet patterns come from all over the world, and each region labels hooks differently. The United States uses letters and numbers like H/8 or K/10.5. Most of the world lists the exact shaft diameter in millimeters, such as 5.0 mm. The UK (and older Canadian and Australian patterns) use a numbering system that runs backwards — bigger numbers mean smaller hooks. This converter lines all three up so a pattern written in one system is easy to follow with the hooks you already own.

Why millimeters are the safe reference

US letters can drift slightly between brands, and a couple of sizes (like G/6, which some brands cut at 4.0 mm and others at 4.25 mm) don't map perfectly. The millimeter measurement is the true, physical size of the hook, so when a pattern and your hook disagree, trust the mm value and check your gauge swatch before starting a project.

How to use it

1. Open the drop-down and choose the hook size named in your pattern.
2. Read the three cards below for the matching Metric (mm), US, and UK values.
3. Prefer to type? Enter a millimeter size in the mm box and the tool snaps to the closest standard hook.
4. A dash (–) means there is no standard equivalent in that system for that size.

FAQ

What size is a US H hook?

A US H/8 hook is 5.0 mm, which is UK size 6 — one of the most common all-purpose crochet hooks.

Why do UK numbers get smaller as the hook gets bigger?

The old UK system was based on wire gauges, where higher numbers meant thinner metal. It runs opposite to the mm scale, so always double-check with the millimeter value.

Are these conversions exact?

They follow the standard Craft Yarn Council chart, but hooks vary slightly by brand. Treat the results as a close guide and confirm with a gauge swatch.

Does this work for steel thread hooks?

This chart covers standard yarn hooks. Tiny steel hooks for thread crochet use a separate numbering system and are not included here.