Crochet hook sizes UK: mm, old UK and US chart

The short answer

Use the millimetre size. The Craft Yarn Council, the US industry body that publishes the hook size standard, tells crocheters to rely on the mm figure on the packet because letter and number sizing varies from company to company. UK shops work the same way. Wool Warehouse, for one, lists its hooks by diameter in mm.

The two other systems you’ll meet in UK patterns are US sizes, a letter plus a number such as H-8, and the old UK numbers found in older British leaflets. Old UK numbers run backwards, so a bigger number means a thinner hook. A size 14 is 2mm and a size 000 is 10mm.

How the chart was put together

Each column has its own source. The US column is the Craft Yarn Council’s Hooks & Needles table. The old UK column comes from three published charts: the Hobbii conversion chart, Sarah Maker’s hook size chart and The Crochet Crowd’s conversion list. Where all three agree we give one number. Where they differ we give both and say who said what. The Japanese column is taken from the manufacturer Tulip’s own size list for its Etimo hooks, with Clover Japan’s jumbo hooks for 7mm and up.

We haven’t measured any hooks ourselves. Every figure here is the publisher’s or the maker’s, and every page is linked at the bottom so you can check it. Wikipedia’s crochet hook article repeats the Craft Yarn Council’s US sizes, and we used it only as a cross-check.

Where published charts disagree

For old UK numbers, the disputed sizes sit between 2.5mm and 3.75mm. The Crochet Crowd makes 2.75mm a UK 11, while Hobbii and Sarah Maker make it a 12. Sarah Maker leaves 2.5mm and 3.5mm without a UK number, while Hobbii and The Crochet Crowd call them 12 and 9. So a UK 12 can mean 2.5mm or 2.75mm, a UK 11 can mean 2.75mm or 3mm, and a UK 9 can mean 3.5mm or 3.75mm, depending on the chart. If an old pattern calls for a number 9, 11 or 12, make a tension square before you commit.

US labels also drift at the big sizes. The Craft Yarn Council gives 9mm as M/N-13 and 10mm as N/P-15. Hobbii prints N-13 and P-15, and LoveCrafts prints M-13 and N-15. In those three charts the number after the letter stays the same, 13 for 9mm and 15 for 10mm, so read that, or better, the mm.

The Craft Yarn Council also lists in-between sizes, such as 4.25mm (G) and 5.25mm (I). Sarah Maker labels the 4.25mm G as a Boye size, and The Crochet Crowd warns that Boye labels its 5.25mm hook I/9, the same label the Council gives to 5.5mm. That small gap is enough to change your tension, so check the mm on the shaft.

Why old UK numbers run backwards

Wikipedia’s knitting needle article says old UK needle numbers were Standard Wire Gauge sizes, the gauge of the wire metal needles were made from. Thinner wire had a higher number. The old crochet hook numbers in the three charts follow the same gauge closely, from 14 at 2mm to 00 at 9mm. Standard Wire Gauge 8 is 4.064mm, which matches the 4mm hook called UK 8. Gauge 10 is 3.251mm, a near match for the 3.25mm UK 10. Gauge 14 is 2.032mm, matching the 2mm UK 14.

We think that also helps explain the disputed rows. A 2.75mm hook sits between gauge 12 (2.642mm) and gauge 11 (2.946mm), and is closer to 12. A 3.5mm hook sits between gauge 10 (3.251mm) and gauge 9 (3.658mm), and is closer to 9. That is our own comparison against Wikipedia’s wire gauge table, not a published standard or rule, though it matches the majority of the three charts in both cases.

Japanese hook sizes

Japanese hooks are labelled with a number followed by /0. Tulip’s size list for its Etimo cushion grip hooks runs from 2/0 at 2.00mm to 10.5/0 at 6.50mm, including half sizes such as 4.5/0 at 2.75mm and 7.5/0 at 4.50mm. Above that, Clover Japan sells jumbo hooks labelled in plain millimetres: 7, 8, 10, 12 and 15mm.

Two charts aimed at English speakers differ from Tulip’s list. Hobbii and Sarah Maker put 3/0 at 2.25mm, where Tulip makes it 2.20mm. Sarah Maker also puts 7/0 at 4.5mm, but both Tulip and Hobbii put 7/0 at 4.00mm and 7.5/0 at 4.50mm. If you’re following a Japanese pattern, go by the maker’s list.

Which sizes come in hook sets

We checked the sizes in five sets on the makers’ own pages, four from Prym and one from Tulip. None of them includes 2.75mm, 3.25mm or 3.75mm, the US sizes C-2, D-3 and F-5. None includes 5.5mm either, the US I-9. If a US pattern asks for one of those, you may need to buy a single hook. Pony’s grey aluminium hooks, sold on cards, include a 3.25mm, and Wool Warehouse lists Pony bamboo hooks in 5.5mm.

The 4mm hook appears in four of the five sets, and 5mm in all five.

Old patterns often give yarn in grams or ounces with a long-gone yarn name. Our grams-to-metres converter turns the grams into metres so you can match a yarn you can buy today. Which hook suits which yarn is a separate question, and the ball band is the place to start, since it often suggests a hook size in mm.

Steel and thread hooks

Steel hooks for crochet thread are numbered the other way round from US yarn hooks: the higher the number, the smaller the hook. The Craft Yarn Council gives the range as #14 at 0.9mm, the smallest, to 00 at 2.7mm, the largest, and says numbering varies between makers.

The published tables bear that out. The Council’s own steel table puts 14 against both 0.90mm (14/8) and 0.75mm (14/10). LoveCrafts lists US steel 14 as 0.75mm, and Hobbii lists it as 0.60mm. Buy thread hooks by the mm, and match the mm your pattern gives.

Common questions

Sources and scope

• www.craftyarncouncil.com/standards/hooks-and-needles
• www.craftyarncouncil.com/standards/steel-crochet-hook-crochet-thread-sizes
• en.wikipedia.org/wiki/Crochet_hook
• en.wikipedia.org/wiki/Knitting_needle
• en.wikipedia.org/wiki/Standard_wire_gauge
• hobbii.co.uk/blogs/news/crochet-hook-conversion-chart
• sarahmaker.com/crochet-hook-sizes/
• thecrochetcrowd.com/crochet-hook-sizes-conversions/
• www.stitchandstory.com/blogs/crochet-tips/crochet-conversion-tables
• www.lovecrafts.com/en-gb/pages/crochet-conversion-tables
• www.tulip-japan.com/
• en.tulip-japan.co.jp/knitting_needle/
• clover.co.jp/product_cat/crochet
• www.prym.com/en/crochet-hooks-for-wool-set-with-soft-handle-2-6mm-7741cb7fce1d9689106a36b5fa4e320a
• www.prym.com/en/crochet-hook-set-alu-coloured-2.5-5.0-mm-36535c233872bfff2d01214a6fa7fd6c
• www.prym.com/en/crochet-hook-for-wool-set-prym.ergonomics
• www.prym.com/en/crochet-hook-set-pop
• ponyneedles.com/product/grey-anodised-aluminium-crochet-hooks/
• www.woolwarehouse.co.uk/needles-and-hooks/pony-single-end-crochet-hook-bamboo-15cm-4-00mm

Sources checked 1 October 2026. Label facts come from the linked references; worked purchase examples and arithmetic are our own illustrations.