Metric to UK to US crochet hook conversion chart

The size of a crochet hook corresponds to specific weights of yarn, and crochet patterns usually list a suggested hook size to help you make the pattern as close to the original design as possible.

Yarn labels also list a hook size or range of sizes that are recommended to work with that particular yarn, though these tend to show for knitting needles (but the size is the same for crochet hooks).

Crochet hook sizes are not completely standardised.

Crochet evolved as a folk art over time, and across continents, hook sizes evolved separately. Crochet hooks can be measured in either letters (US), numbers (UK/US) or metric units (millimetres).


What if my crochet hook size is not labelled?

Sometimes crochet hooks are not labelled with a size, which can be frustrating.

If you inherited some hooks from your gran, this might be the case.

You can easily measure the hook size with a knitting needle and crochet hook gauge tool that has holes drilled to specific millimetre measurement.

Just insert your hook into the hole until you find the one that fits, and then you’ll know exactly what size you’re working with.

What are crochet thread hook sizes?

Steel crochet hooks are the smallest hooks and are not represented on the standard size crochet hook size conversion chart.

These hooks are used for fine thread crocheting, like lace or doilies, and usually used with crochet thread.

They are made of a stronger metal (steel) to keep the tiny hooks from bending while you work. Steel hooks generally have very sharp ends and many steel crochet hooks come with a metal cover to protect the end of the hook.

These can sometimes also be used to join crochet to fabric because they’re so sharp.

If you are using crochet thread and steel crochet hooks, they are measured a different way because of their tiny size.

For the metric system, crochet hooks are still measured in millimetres, but US thread hooks are measured in a number system that gets higher as the hook gets smaller.

What are Tunisian crochet hooks?

A Tunisian crochet hook is a specialised tool used for Tunisian crochet, also known as Afghan crochet.

Tunisian crochet is known for its unique fabric texture and variety of stitches that can mimic knitting or weaving.

The technique typically involves a “forward pass” where loops are collected onto the hook and a “return pass” where they are worked off.

This creates a denser, often more textured fabric than traditional crochet.

Tunisian crochet hooks are integral to this craft, enabling the distinctive techniques and stitches unique to Tunisian crochet.

Tunisian crochet hooks are typically longer than traditional crochet hooks. They can range from 10 inches to 14 inches or even longer.

The extra length allows for more loops to be held on the hook simultaneously, as Tunisian crochet often involves picking up a large number of loops and holding them on the hook.

Traditional Tunisian crochet hooks have a stopper at the end to prevent stitches from slipping off. The stopper can be a simple knob or a wider end similar to a knitting needle.

Some Tunisian hooks have an extension cable at the end (similar to circular knitting needles) to hold a large number of stitches, which is helpful for making larger items like blankets or garments.

The flexible cable allows the weight of the project to rest in the lap, reducing the strain on the wrists and hands.

There are also double-ended Tunisian crochet hooks, which allow for working in the round or using two colours of yarn.

These hooks have a head at each end, sometimes with one end slightly larger than the other.

Tunisian hooks are made from various materials, including aluminium, plastic, bamboo, or wood.

Some are ergonomically designed with handles that are easy to hold and reduce hand fatigue.

Tunisian crochet hooks are sized similarly to regular crochet hooks, but there are a few specifics to keep in mind:

  1. Diameter: Like traditional crochet hooks, the diameter of the Tunisian crochet hook determines its size. The diameter affects the size of the stitches and, consequently, the final fabric. Tunisian hooks follow the same sizing conventions, using either millimetres for metric sizes or numbered or lettered systems for U.S. sizes.
  2. Length: Tunisian crochet hooks are longer than regular crochet hooks because the technique involves holding multiple loops on the hook simultaneously, much like knitting. The lengths can vary significantly, from about 10 inches to 14 inches for standard hooks, and much longer for those designed to handle larger projects. There are also Tunisian hooks with cables attached, similar to circular knitting needles, to accommodate a high number of stitches.
  3. Markings: Like regular crochet hooks, the size is usually marked on the hook itself. If the marking has worn off or is not visible, you would use the same methods to determine the size as you would with regular crochet hooks (such as a hook gauge tool or measuring the diameter).
  4. Materials: They can be made of the same variety of materials as regular crochet hooks, such as aluminium, plastic, bamboo, or wood. The material doesn’t change how the size is determined, but it can affect the grip and the weight of the hook.

As with any craft, the more you work with the tools, the better you’ll become at understanding and feeling the subtle differences between sizes.

If you’re working on a specific project, it’s always good practice to create a gauge swatch first to make sure that your hook size is giving you the correct tension and fabric texture.