Crochet Hook Size Chart

What the Markings on a Crochet Hook Mean

Pick up a crochet hook and you will usually find two or three sizes stamped on the thumb rest: a millimetre measurement, a US letter, and a US number. They describe the same hook, but they do not derive from one another. The letter and number are a labelling convention; the millimetre figure is the actual diameter of the shaft, measured where the yarn rides. A hook marked "H/8" and "5.0 mm" is one hook with three names.

The millimetre measurement is the one to trust. The Craft Yarn Council, which sets the US standard, says plainly that letter and number sizing varies from company to company and that you should rely on the package millimetre figure. That is why this converter is anchored on millimetres: enter a size in any system and it resolves to the diameter first, then to the labels other makers would recognise. If you have already settled on a hook and want to plan the project around it, the granny square calculator and the yarn yardage calculator take over from there.

The Crochet Hook Size Chart

The table below lists the regular yarn-hook sizes most patterns use, with the millimetre diameter as the spine and the US and old UK equivalents beside it. A few rows carry a note, because the old UK scale does not map cleanly onto every metric size and an honest chart says so rather than hiding it.

Two rows are worth a second look. The 2.75 mm hook is shown as UK 11 here, but sources genuinely disagree: some charts put UK 11 at 3.0 mm and label 2.75 mm as a UK 12, because the coarse old scale has no exact 2.75 mm step. The single UK 9 hook, likewise, sits somewhere between 3.5 and 3.75 mm depending on the chart you read. At the large end the US letters above 9 mm shift by brand while the US numbers hold steadier. None of this trips you up if you read the millimetre figure off the package.

Why "Size H" Is Not the Same Hook Everywhere

The most useful thing this page can tell you is that a US letter on its own is not a reliable size. Two of the biggest hook makers, Susan Bates and Boye, assign different millimetre diameters to the same letter. The gap is small, but it is real and it is enough to move your gauge.

• Size G is 4.00 mm on a Susan Bates hook and 4.25 mm on a Boye.
• Size I is 5.50 mm on a Bates and 5.25 mm on a Boye.
• Size J is 6.00 mm on a Bates and 5.75 mm on a Boye.

So a pattern that calls for "a size I hook" is really asking for somewhere between 5.25 and 5.50 mm, and the two brands sit on opposite sides of that. The practical rule is the one the standards body gives: the same letter can map to slightly different millimetres across brands, so go by the millimetre figure printed on the package, not the letter alone. These per-brand numbers come from the manufacturers' own packaging and product labelling rather than a published corporate specification chart, so treat them as accurate to the hooks on the shelf rather than as a sealed standard.

The Old UK Numbers Run Backwards

British patterns from before metric sizing took hold use a numbering scale that catches everyone out the first time: the bigger the number, the smaller the hook. A UK 14 is a fine 2 mm hook, while a UK 1 is large. The scale descends as the hook grows, which is the reverse of the US number scale, where bigger means bigger.

The reversal is not arbitrary. The old UK sizes come from the imperial Standard Wire Gauge, the same system once used to measure wire and knitting-needle diameters, and that gauge was numbered in the opposite order to the French gauge it competed with: a larger number meant a thinner wire. Crochet hooks inherited the convention, which is why a vintage British pattern's "No. 8 hook" is a middling 4 mm rather than something tiny. The yarn weight guide covers the matching reversal in old UK ply names, where the wording shifts the same way the numbers do.

Steel Hooks Use a Separate, Reversed Scale

Steel crochet hooks, used for thread crochet, lace, and doilies, sit on their own scale, and it is easy to mistake one for a regular hook. They run from about 3.5 mm down to under 1 mm, and like the old UK numbers they run backwards: a higher steel number is a finer hook. The Craft Yarn Council lists the smallest, a US steel 14, at 0.90 mm.

The trap is that the steel numbers overlap the regular ones while meaning something completely different. A steel "size 2" is a 2.25 mm thread hook; a regular "US 2" is a 2.75 mm C hook. They are not the same tool, and a pattern that wants a steel hook will say so. This converter keeps the two scales apart for exactly that reason, so a steel size never resolves to a regular hook by accident.

Material and Grip

Beyond size, the material a hook is made from changes how it feels in the hand and how fast the yarn slides. The differences are a matter of preference rather than correctness, but they are worth knowing.

• Aluminium is smooth and quick, which suits sticky yarns such as acrylic.
• Steel is used for the fine thread hooks and the smallest sizes.
• Wood and bamboo have a slight grip that helps with slippery fibres like silk.
• Plastic is light and inexpensive, and the usual choice for the largest hooks.
• Ergonomic handles add a soft grip that eases hand strain over a long session.

Material does not change the size on the chart: a 5 mm aluminium hook and a 5 mm wooden hook are the same diameter, and a pattern's hook recommendation is about size, not what the hook is made from.

The Size Is a Starting Point, Not the Last Word

Every figure on this page gets you close, and the millimetre column gets you closest of all. But the size printed on a hook is a starting point, not a promise of how your fabric will turn out, because tension varies from one crocheter to the next. The same 5 mm hook in two pairs of hands produces two slightly different gauges.

So the honest last step is always the same. The equivalence tells you which hook to reach for, the millimetre figure tells you what it truly measures, and your gauge swatch has the final word on whether it makes the fabric the pattern intends. Work a square in the yarn and hook you mean to use, measure it, and check it against the pattern with the gauge swatch calculator. If the gauge is off, move to a different hook size and swatch again — the chart above will tell you exactly which size you are stepping to.