Crochet Hook Size Chart: US, UK and Metric Guide

Quick answer: Crochet hook sizes are easiest to compare by shaft diameter in millimeters. US letters and numbers are useful labels, but they are not perfectly consistent between manufacturers, and old UK or Canadian numbers can be even more confusing. Start with the pattern’s stated millimeter size, then make a gauge swatch with the actual yarn before committing to the project.

If you need to decode a marking such as H/8, UK 6, or steel 10, the interactive Crochet Hook Size Chart shows metric, common US, and historical UK/Canadian equivalents while flagging labels that have more than one possible meaning. That ambiguity warning matters: a conversion chart is a starting point, not a substitute for measuring the hook and checking gauge.

Crochet hook size chart

The following table covers widely used regular crochet hook sizes. Metric diameter is the safest column to use when a pattern, package, and hook seem to disagree.

These are practical cross-references, not manufacturing tolerances. The Craft Yarn Council specifically advises relying on millimeters because letter and number designations can vary by company. If your hook is marked only with a letter, check the manufacturer’s own packaging or measure the straight shaft.

Why crochet hook sizing is confusing

Crochet hooks are sold through several overlapping systems. Metric sizing describes the shaft diameter directly. A 5.0 mm hook is intended to have a 5.0 mm working shaft, which makes the label portable across countries and brands.

The common US system combines letters and numbers, such as G/6, H/8, and I/9. Those pairings are familiar, but the sequence is not perfectly continuous. A 4.5 mm hook may simply be labeled “7,” while some intermediate diameters have a letter without a stable paired number. Manufacturers have also used the same letter for slightly different diameters.

Older UK and Canadian patterns often use descending numbers: a larger number generally points to a smaller regular hook. Modern UK patterns increasingly state millimeters, which removes much of the uncertainty. Historical charts still disagree on some conversions, so treat an old number as a clue and verify the diameter.

Always use millimeters as the anchor

If a pattern says “US H/8 (5 mm),” the 5 mm measurement is the most dependable part. If your H hook measures 5.25 mm, it is not the same working size for that pattern even though the letter looks right.

Measure across the straight shaft—the section that controls the size of the loops. Do not measure the hook head, throat, thumb rest, or ergonomic handle. A physical slotted hook gauge is convenient, while a caliper can help with an unmarked hook. On-screen gauges are useful only after careful calibration and should not be treated as certified measuring tools.

Metric-first comparison is especially helpful when buying replacement hooks, reading imported patterns, sorting inherited tools, or switching between brands. Write the millimeter size on your project notes so you can reproduce the fabric later.

Regular hooks and steel hooks are different systems

Do not mix regular yarn-hook numbers with steel crochet-hook numbers. Steel hooks are designed mainly for crochet thread and fine lace work. In the common US steel system, a higher number means a smaller hook—the reverse of the way many people expect ordinary tool sizing to behave.

Steel labels are also unusually ambiguous. A “steel 10” may refer to different diameters depending on the manufacturer or chart. The Craft Yarn Council’s published steel table contains repeated numbers at different metric sizes, which is a strong reason to inspect the millimeter marking or measure the hook directly.

A steel size 6 is not the same thing as a regular US G/6. The shared number is coincidental. Before converting, identify the hook family: regular hooks usually work with yarn and have larger shafts; steel hooks are slender and commonly used with thread.

How yarn weight relates to hook size

Yarn weight gives you a starting range, not a mandatory hook size. The Craft Yarn Council’s yarn-weight guidance pairs common categories with broad metric ranges:

• Lace: often steel hooks around 1.4–1.6 mm for thread, or a regular hook around 2.25 mm; open lace may deliberately use a much larger hook.
• Super fine: approximately 2.25–3.5 mm.
• Fine: approximately 3.5–4.5 mm.
• Light: approximately 4.5–5.5 mm.
• Medium: approximately 5.5–6.5 mm.
• Bulky: approximately 6.5–9 mm.
• Super bulky: approximately 9–15 mm.
• Jumbo: 15 mm and larger.

The yarn label may recommend a different range, and the pattern designer may choose a hook outside it to create a particular fabric. Amigurumi often uses a smaller hook for a dense surface that hides stuffing. Shawls and open lace may use a larger hook for drape and negative space.

Gauge decides whether the hook is right

A correct conversion does not guarantee a correctly sized project. Two crocheters can use the same yarn and 5 mm hook yet produce different stitch counts because of tension, grip, hook style, and stitch formation.

Make the swatch specified by the pattern. Use the stated stitch pattern rather than substituting single crochet unless the instructions permit it. Make the swatch larger than the measuring area, then wash or block it the way the finished item will be treated. Measure the central section after it has rested.

If you have fewer stitches than the pattern calls for across the measured width, your stitches are too large; try a smaller hook. If you have more stitches, your stitches are too small; try a larger hook. Re-swatch after each change. Row gauge can also affect sleeve length, armholes, and shaped sections, even when stitch gauge is correct.

How to convert an old pattern safely

1. Identify the pattern’s country and date. A bare “size 6” can mean different things in US regular, US steel, and old UK systems.
2. Look for a millimeter value. Use it ahead of the letter or number.
3. Identify the hook family. Thread and doily instructions may imply a steel hook.
4. Check more than one reputable chart. If the old label maps to several diameters, preserve that uncertainty.
5. Compare yarn and finished gauge. Older yarn names may not line up neatly with modern weight categories.
6. Swatch candidate sizes. The hook that produces the pattern gauge and suitable fabric is the practical answer.

Do not average conflicting conversions. If one reference maps a label to 2.75 mm and another maps it to 3.0 mm, those are two candidates to test, not a mathematical invitation to buy a 2.875 mm hook.

Does hook material change the size?

Aluminum, steel, bamboo, wood, resin, and plastic hooks can share the same nominal diameter. Material does not change what 5 mm means, but it can change how the yarn slides and how tightly you work. A polished metal hook may feel faster than a grippy wood hook. An ergonomic handle can reduce hand pressure without changing the working shaft.

Hook shape matters too. Inline and tapered heads catch and release yarn differently, and the throat length can affect how loops are formed. When exact gauge matters, swatch with the actual hook you plan to use—not merely another hook bearing the same size label.

Common crochet hook conversion mistakes

• Reading H/8 as 8 mm: H/8 is a common US label for a 5.0 mm hook; the “8” is not its metric diameter.
• Trusting a letter more than millimeters: letters can vary by brand.
• Confusing regular and steel hooks: their number systems are unrelated.
• Assuming yarn weight determines one hook: recommended ranges are only starting points.
• Measuring the hook head: the straight shaft controls loop size.
• Skipping the blocked swatch: fibers can relax, bloom, stretch, or shrink after washing.
• Using an on-screen ruler without calibration: browser zoom and display density can distort physical scale.
• Changing hook size but ignoring fabric: matching gauge is not useful if the result is too stiff or too open for the project.

Frequently asked questions

What size is an H crochet hook?

A common US H/8 hook is 5.0 mm. Because manufacturer labels can vary, confirm the millimeter marking on the package or measure the shaft.

What size is a G crochet hook?

US G/6 commonly means 4.0 mm, but some manufacturers use G for 4.25 mm. The metric size resolves the difference.

What crochet hook should a beginner use?

A 5.0 or 5.5 mm regular hook with smooth, light-colored medium-weight yarn is often manageable for practice because the stitches are easy to see. For a real project, follow the pattern and yarn label, then check gauge.

Can I use a larger crochet hook than the pattern says?

Yes, but the fabric will usually become looser and the finished dimensions may grow. A larger hook can be intentional for drape or lace. Swatch first and recalculate only if you understand how the change affects gauge and yardage.

How can I identify an unmarked crochet hook?

Measure the straight shaft with a physical hook gauge or caliper. Avoid the head and handle. Then compare the measured millimeters with a chart; do not assign a US letter if the diameter falls between brand conventions.

Are UK and US crochet terms the same?

No. Hook sizing and stitch terminology are separate issues, and both can differ. A UK double crochet is a US single crochet, for example. Confirm the pattern’s terminology as well as the hook diameter.

The bottom line

A crochet hook size chart is most useful when it exposes uncertainty rather than hiding it. Convert the label to millimeters, identify whether the hook is regular or steel, measure the working shaft when necessary, and finish with a blocked gauge swatch. The chart helps you choose a candidate; the swatch tells you whether that candidate works for your hands, yarn, and pattern.

Sources: Craft Yarn Council: Hooks & Needles; Craft Yarn Council: Steel Crochet Hooks; Craft Yarn Council: Standard Yarn Weight System; Clover: Swatch Ruler and Hook Gauge; Yarnspirations: How to Measure Crochet Gauge.