Crochet Hook Sizes & Size Chart: US, Metric (mm) & UK Guide

Understanding crochet hook sizes is the single most important skill for hitting accurate pattern gauge, achieving even stitch definition, and making sure your finished sweaters, blankets, and amigurumi plushies match the exact measurements in your pattern.

However, crochet hooks sizes can quickly feel overwhelming because different regions and manufacturers use four completely different sizing systems:

• US Crochet Hook Sizes use letters and numbers (such as a size C crochet hook C-2, a size 6 crochet hook letter G-6, a 5.0 crochet hook letter H-8, a crochet I hook mm I-9, or a size 10 J-10).
• Metric Crochet Hook Sizes measure the exact hook shaft diameter in millimeters (2.25 mm, 2.75 mm, 4.0 mm, 5.0 mm, 5.5 mm, 6.0 mm, 10.0 mm).
• UK & Canadian Hook Sizes use reverse wire-gauge numbers (where UK #14 is tiny and UK #000 is jumbo).
• Steel Lace Hook Sizes use a reversed number system (00 to 14) where higher numbers mean smaller hooks—so a size 10 crochet hook in mm for lace thread is 1.15 mm – 1.30 mm!

In this master crochet hook size chart and crochet hooks conversion chart guide, you will find instant answers to the most-searched hook size conversions, a complete crochet hooks sizes conversion chart (US, Metric mm, UK, and Steel), yarn-to-hook matching charts, an anatomical guide to inline vs. tapered hooks, and our complete Crochet Hook Buying Guide & Topic Wrap-Up.

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⚡ Instant Answers: Most-Searched Crochet Hook Sizes & Letter Conversions

Before scrolling to the full crochet hook size chart, here are direct, Featured-Snippet-ready answers to the most common crochet hook sizes and letter-to-millimeter questions:

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📊 Crochet Hook Size Chart (Master Crochet Hooks Sizes Conversion Chart)

Use this complete crochet hook size chart and crochet hooks sizes conversion chart to convert between US Letters/Numbers, Metric Millimeters (mm), UK / Canadian Numbers, and Recommended Yarn Weights:

US Size (Letter / Number)	Metric Size (mm)	UK / Canadian Size	Recommended Yarn Weight	Typical Gauge (sc per inch)	Ideal Crochet Projects
B-1	2.25 mm	13	Weight 0–1 (Lace / Fingering)	7 – 8 sc	Fine lace, baby booties, micro amigurumi
C-2 (Size C Crochet Hook)	2.75 mm	11 or 12	Weight 1–2 (Fingering / Sport)	5.5 – 7 sc	Lightweight shawls, socks, fine amigurumi
D-3 (UK Size 10)	3.25 mm	10	Weight 2 (Fine / Sport)	5 – 6 sc	Baby garments, lightweight summer tops
E-4	3.50 mm	9	Weight 2–3 (Sport / DK)	4.5 – 5.25 sc	Amigurumi plushies, granny motifs
F-5	3.75 mm	8	Weight 3 (Light / DK)	4 – 4.75 sc	Light cardigans, baby blankets
G-6 (Size 6 Crochet Hook Letter)	4.00 mm (or 4.25 mm)	8	Weight 3–4 (DK / Worsted)	3.75 – 4.5 sc	Hats, amigurumi, market tote bags
7 (No US Letter)	4.50 mm	7	Weight 3–4 (DK / Worsted)	3.5 – 4.25 sc	Textured sweaters, drapy scarves
H-8 (5.0 Crochet Hook Letter)	5.00 mm	6	Weight 4 (Medium / Worsted)	3 – 3.75 sc	#1 Beginner staple, blankets, hats
I-9 (Crochet I Hook mm)	5.50 mm	5	Weight 4 (Worsted / Aran)	2.75 – 3.5 sc	Cozy plaid blankets, scarves, totes
J-10 (Size 10 Yarn Hook)	6.00 mm	4	Weight 4–5 (Heavy Worsted / Bulky)	2.5 – 3 sc	Chunky beanies, thick winter cowls
K-10.5 (10½ Hook)	6.50 mm	3	Weight 5 (Bulky / Chunky)	2.25 – 2.75 sc	Quick chunky throw blankets, baskets
L-11	8.00 mm	0	Weight 5–6 (Bulky / Super Bulky)	1.75 – 2.25 sc	Plush chenille velvet blankets, rugs
M/N-13	9.00 mm	00	Weight 6 (Super Bulky)	1.5 – 2 sc	Super bulky cowls, pet beds
N/P-15 (10.0 mm Hook)	10.00 mm	000	Weight 6 (Super Bulky)	1.25 – 1.75 sc	Giant winter scarves, floor poufs
P/Q	15.00 mm	—	Weight 7 (Jumbo)	1 – 1.25 sc	Chunky rope baskets, thick rugs
Q	16.00 mm	—	Weight 7 (Jumbo)	0.75 – 1 sc	Heavy jumbo yarn throws
S	19.00 mm	—	Weight 7 (Jumbo)	0.5 – 0.75 sc	Giant statement blankets
T / U / X	25.00 mm – 30.00 mm	—	Weight 7 (Extreme Jumbo)	< 0.5 sc	Extreme roving & rag rugs

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🪡 Steel Crochet Hooks Conversion Chart (Size 10 Crochet Hook in mm & Lace Sizes)

When working with fine mercerized cotton thread (such as Size 10, 20, or 30 crochet thread) for snowflakes, doilies, tablecloths, or bead crochet, standard aluminum hooks are too thick. Instead, you use a steel micro crochet hook.

[!WARNING] Steel Hook Numbers Run Backwards! In steel crochet hook sizes, higher numbers equal smaller millimeter sizes. When a lace pattern calls for a “size 10 crochet hook in mm”, it means a US Steel Size 10 (1.15 mm – 1.30 mm)—NOT a 6.0 mm (J-10) or 10.0 mm (N/P-15) yarn hook!

Use this steel crochet hooks conversion chart to match US steel numbers, UK steel sizes, and metric millimeters (mm):

US Steel Hook Size	Metric Size (mm)	UK Steel Hook Size	Recommended Crochet Thread / Yarn	Best Project Types
00	3.50 mm	—	Fingering yarn / Heavy Perle Cotton	Thick thread edgings, coasters
0	2.70 mm – 3.25 mm	00	Size 3 & Size 5 Perle Cotton	Sturdy trims, bags, heavy lace
1	2.35 mm – 2.75 mm	0	Size 5 Perle Cotton	Vintage potholders, thick motifs
2	2.20 mm – 2.25 mm	1	Size 5 & Size 10 Crochet Thread	Heirloom snowflakes, collars
3	2.10 mm	1.5	Size 10 Bedspread Cotton Thread	Table runners, bookmarks
4	2.00 mm	2	Size 10 Crochet Thread	Micro amigurumi, lace ornaments
5	1.90 mm	2.5	Size 10 Crochet Thread	Classic doilies, curtain edging
6	1.60 mm – 1.80 mm	2.5	Size 10 & Size 20 Crochet Thread	Crisp Christmas snowflakes
7	1.50 mm – 1.65 mm	3	Size 10 & Size 20 Crochet Thread	Fine lace doilies, tablecloth motifs
8	1.40 mm – 1.50 mm	3.5	Size 20 Crochet Thread	Delicate heirloom lace, beadwork
9	1.25 mm – 1.40 mm	4	Size 20 & Size 30 Crochet Thread	Fine bridal lace, handkerchiefs
10 (Size 10 Steel in mm)	1.15 mm – 1.30 mm	4.5	Size 30 Crochet Thread	Intricate thread medallions, beads
11	1.00 mm – 1.10 mm	5	Size 30 & Size 40 Thread	Micro lace edging
12	0.75 mm – 1.00 mm	5.5	Size 40 & Size 50 Thread	Ultra-fine tatted-look lace
13	0.75 mm – 0.85 mm	6	Size 60 & Size 70 Thread	Miniature dollhouse crochet
14	0.60 mm – 0.75 mm	6.5	Size 80 – 100 Micro Thread	Micro bead crochet & fine jewelry

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🔎 Deep-Dive: The 5 Most Confusing Crochet Hook Sizes Explained

Why do so many crocheters search a crochet hooks conversion chart for the exact same five hook sizes? Because US letters, UK numbers, and metric millimeters overlap in tricky ways! Here is a complete breakdown of the top 5 most-searched crochet hook sizes:

1. Size C Crochet Hook (US C-2 = 2.75 mm)

• Metric Equivalent: 2.75 mm (occasionally 2.50 mm in vintage European sets).
• UK Equivalent: UK Size 11 (or UK Size 12).
• When to Use a Size C Crochet Hook: A size C crochet hook is the gold-standard tool for Super Fine (#1) Fingering and Fine (#2) Sport weight yarn. It is also the #1 choice for crocheters making miniature amigurumi keychains with DK (#3) cotton yarn because the 2.75 mm shaft creates ultra-tight, gap-free stitches.

2. Size 6 Crochet Hook Letter (US G-6 = 4.0 mm vs. 6.0 mm J-10 vs. UK 6)

When someone searches for the “size 6 crochet hook letter”, they could be looking at three completely different hooks depending on where their pattern was written:

1. US Size 6 (G-6 — 4.0 mm / 4.25 mm): In American patterns, the number 6 is paired with Letter G (G-6), which measures 4.0 mm in Susan Bates/Clover hooks and 4.25 mm in Boye hooks.
2. Metric 6.0 mm Hook (US J-10): If your hook says 6.0 mm on the thumb rest, its US letter is Letter J (J-10)!
3. UK Size 6 Hook (5.0 mm / US H-8): If you are reading a vintage British or Canadian pattern calling for a “Size 6 hook,” it means a 5.0 mm (US Letter H-8) hook!

3. 5.0 Crochet Hook Letter (US H-8 = 5.0 mm)

• US Letter Equivalent: Letter H (H-8).
• UK Equivalent: UK Size 6.
• Why the 5.0 Crochet Hook Letter is #1: Ask any instructor which hook to buy first, and the answer is always a 5.0 mm (US H-8) hook. Paired with Medium (#4) worsted weight yarn, it produces roughly 3 to 3.75 single crochets per inch—giving you clear, easy-to-count V-stitches without straining your wrists.

4. Crochet I Hook mm (US I-9 = 5.5 mm)

• Metric Equivalent: 5.5 mm.
• UK Equivalent: UK Size 5.
• When to Use an I-9 (5.5 mm) Hook: Stepping up just 0.5 mm from an H-8 (5.0 mm) to a crochet I hook (5.5 mm) gives worsted-weight fabric a softer, squisher drape. That is why our Evermore Plaid Granny Square Blanket and Beginner Market Tote Bag both use a 5.5 mm (US I-9) hook!

5. Size 10 Crochet Hook in mm (1.15 mm vs. 6.0 mm vs. 10.0 mm)

Never guess when a pattern says “Size 10 crochet hook”—check which of these four hooks matches your yarn:

• Thread / Lace Pattern (US Steel Size 10): Measures 1.15 mm – 1.30 mm (Boye is 1.30 mm, Susan Bates is 1.15 mm).
• US Yarn Pattern (US J-10): Measures 6.0 mm (or 6.5 mm for K-10.5).
• UK Yarn Pattern (UK Size 10): Measures 3.25 mm (US D-3).
• Super Bulky Pattern (10.0 mm): Measures 10.0 mm (US N/P-15).

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🧶 Recommended Crochet Hook Size for Each Yarn Weight

Matching your yarn weight to the right entry on the crochet hook size chart ensures your fabric isn’t stiff as cardboard or floppy and holey. Use this Craft Yarn Council reference table to match yarn weights (#0 to #7) with crochet hooks sizes and stitch gauges:

Yarn Weight Symbol & Category	Common Yarn Names	Recommended Metric Hook (mm)	Recommended US Hook Letter	Average Gauge (Single Crochet per Inch)
#0 — Lace	Fingering 10-count thread	1.40 mm – 2.25 mm	Steel 8 to B-1	8+ sc per inch
#1 — Super Fine	Sock, Fingering, Baby	2.25 mm – 3.50 mm	B-1 to E-4	5.25 – 8 sc per inch
#2 — Fine	Sport, Baby	3.50 mm – 4.50 mm	E-4 to 7	4 – 5 sc per inch
#3 — Light	DK (Double Knitting), Light Worsted	4.50 mm – 5.50 mm	7 to I-9	3 – 4.25 sc per inch
#4 — Medium	Worsted, Afghan, Aran	5.00 mm – 6.50 mm	H-8 to K-10.5	2.75 – 3.5 sc per inch
#5 — Bulky	Chunky, Craft, Rug	6.50 mm – 9.00 mm	K-10.5 to M/N-13	2 – 2.75 sc per inch
#6 — Super Bulky	Super Bulky, Roving	9.00 mm – 16.00 mm	M/N-13 to Q	1.5 – 2.25 sc per inch
#7 — Jumbo	Jumbo, Arm-Knitting Chenille	15.00 mm and larger	P/Q to S+	Fewer than 1.5 sc per inch

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🏭 Brand-by-Brand Sizing Differences: Why Metric (mm) Beats US Letters

One of the biggest SEO & crafting secrets that most beginner guides leave out is manufacturer letter drift. Even if two hooks are stamped with the exact same US letter, they may be different millimeter sizes depending on the brand!

US Hook Label	Craft Yarn Council / Susan Bates / Clover (mm)	Boye Standard (mm)	Vintage / European Equivalent (mm)
Size B-1	2.25 mm	2.25 mm	2.00 mm
Size C-2 (Size C)	2.75 mm	2.75 mm	2.50 mm
Size D-3	3.25 mm	3.125 mm / 3.25 mm	3.00 mm
Size G-6 (Size 6)	4.00 mm	4.25 mm	4.00 mm
Size I-9 (I Hook)	5.50 mm	5.25 mm / 5.50 mm	5.50 mm
Size K-10.5	6.50 mm	6.50 mm	7.00 mm
Size N-15	10.00 mm	9.00 mm	10.00 mm

[!TIP] How to Measure Unlabeled Hooks: Have vintage or wooden crochet hooks with worn-off labels? Never guess the letter—slide the hook shaft through the round holes of a metal crochet hook gauge tool (or use digital calipers on the straight cylinder between the throat and thumb rest) to find its true millimeter (mm) size!

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🔍 Anatomy of a Crochet Hook: The 5 Parts That Control Your Stitches

Every crochet hook is engineered with 5 distinct anatomical zones. Understanding where the millimeter measurement is taken—and how the head and throat interact with your yarn—will transform your tension:

1. The Point (Head): The tip of the hook that enters your stitch. A more pointed head easily pierces tight single crochet stitches (ideal for amigurumi), whereas a rounded head glides between loops without splitting loosely plied yarns.
2. The Throat & Lip: The cutout hook groove that catches your working yarn and draws it through.
3. The Shaft (Working Area — Sets Your Hook Size!): The straight cylindrical neck behind the throat. This shaft diameter in millimeters (mm) defines your crochet hook size and sets the exact height and width of your yarn loops.
4. The Thumb Rest: The flattened finger grip where the US letter and metric mm size are stamped. It prevents the hook from twisting in your fingers.
5. The Handle: The back shaft that rests inside your hand (whether you use a Pencil Grip or a Knife Grip).

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⚖️ Inline vs. Tapered Crochet Hooks: Which Should You Buy?

When comparing crochet hooks sizes across brands, you will notice two distinct head shapes: Inline (like Susan Bates) and Tapered (like Boye and Clover Amour).

Feature	Inline Crochet Hooks (e.g., Susan Bates)	Tapered Crochet Hooks (e.g., Boye, Clover Amour)
Head Alignment	Head is 100% flush (inline) with the shaft width	Head curves slightly wider than the tapered neck
Throat Shape	Deep, sharply angled notch cut straight into the shaft	Smooth, gradually sloped throat that tapers narrower
Tension Control	Keeps every loop uniform along the straight cylinder	Allows fast, fluid wrist motion without catching yarn plies
Best For	Beginners stabilizing tension, tight amigurumi, cotton	Fast crocheters, splitty multi-ply wool or acrylic yarns
Popular Brands	Susan Bates Silvalume, Furls Streamline, Lykke Driftwood	Clover Amour, Tulip Etimo, Boye, Knitter’s Pride Waves

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🪵 Crochet Hook Buying Guide: Materials, Brands & Tunisian Hooks

Beyond choosing the right millimeter diameter from the crochet hook size chart, the material of your hook controls friction (“drag” vs. “glide”):

1. Ergonomic Soft-Grip Hooks (Clover Amour, Tulip Etimo, Knitter’s Pride Waves, addi Swing): Combine a warm, cushioned elastomer handle with a matte aluminum tip. Best all-around choice for preventing hand cramps and carpal tunnel fatigue.
2. Smooth Aluminum Hooks (Susan Bates Silvalume, Boye, Knitter’s Pride Zing): Lightweight, durable, and fast-gliding. Best paired with “grabby” yarns like 100% wool, mohair, alpaca, and cotton.
3. Warm Wood & Bamboo Hooks (Lykke Blush & Driftwood, Knitter’s Pride Ginger & Dreamz): Provide natural surface grip that slows down slippery fibers like silk, bamboo, rayon, and mercerized cotton so loops never slip off your hook.
4. Plastic & Resin Jumbo Hooks (10.0 mm to 25.0 mm): Lightweight hollow or resin hooks designed for Super Bulky (#6) and Jumbo (#7) yarns so heavy hooks don’t strain your wrists.
5. Tunisian (Afghan) Crochet Hooks: Extra-long hooks (with a stopper cap or flexible interchangeable cord) that hold a full row of stitches like a knitting needle. Rule of thumb: Always size up 1.0 mm to 2.0 mm larger than your regular crochet hook size when working Tunisian crochet!

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🎯 Complete Topic Wrap-Up: The Ultimate Crochet Hook Sizing Cheat Sheet

To wrap up everything covered in this crochet hook sizes and crochet hook size chart master guide, keep these 5 Golden Rules of Crochet Hook Sizing in mind before starting your next project:

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❓ Frequently Asked Questions (Crochet Hook Sizes FAQ)

What letter is a 5.0 crochet hook?

The 5.0 crochet hook letter is US Letter H (written as H-8) and corresponds to a UK Size 6. It is the most popular crochet hook size in the world and is the standard recommendation for Medium Weight #4 worsted yarn.

What is a size 6 crochet hook letter?

Depending on which sizing system your pattern uses, a size 6 crochet hook letter can refer to one of three hooks:

1. US Size 6 (G-6): This is Letter G, which measures 4.0 mm (or 4.25 mm in Boye hooks).
2. Metric 6.0 mm Hook (J-10): A 6.0 mm hook corresponds to US Letter J (J-10).
3. UK Size 6 Hook (H-8): In UK/Canadian sizing, a Size 6 hook measures 5.0 mm (US Letter H-8).

What is a size 10 crochet hook in mm?

Because “10” appears in four different crochet sizing systems on a crochet hooks sizes conversion chart, check your yarn weight to pick the right millimeter size:

• US J-10 Yarn Hook: Measures 6.0 mm (used with Heavy Worsted / Bulky #5 yarn).
• US K-10.5 (10½) Yarn Hook: Measures 6.5 mm (used with Bulky #5 yarn).
• US Size 10 Steel Thread Hook: Measures 1.15 mm to 1.30 mm (used with fine lace crochet thread).
• UK Size 10 Hook: Measures 3.25 mm (US D-3) (used with Sport #2 yarn).
• Metric 10.0 mm Hook: Corresponds to US N/P-15 (used with Super Bulky #6 yarn).

What is a crochet I hook in mm?

The crochet I hook mm measurement is 5.5 mm (written as US I-9), which corresponds to a UK Size 5.

What is a size C crochet hook in mm?

A size C crochet hook (written as US C-2) measures 2.75 mm in metric sizing (and corresponds to a UK Size 11 or 12). It is widely used for sock yarn, sport weight garments, and detailed amigurumi toys.

What is the best crochet hook size for beginners?

A 5.0 mm (US H-8) or 5.5 mm (US I-9) ergonomic crochet hook paired with smooth, light-colored Medium Weight #4 worsted yarn is the best starter size for beginners. The loops are large enough to see clearly, and the handle sits comfortably in your hand.

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🔗 Essential Related Crochet Guides & Patterns

• 🧮 Crochet Hook Conversion Chart (Quick Reference): Bookmark our fast-lookup conversion page for US, UK, and steel hook sizes.
• 🛠️ 10 Essential Crochet Tools for Beginners: Complete checklist of must-have notions beyond your crochet hook.
• 🧶 How to Choose Yarn for Your Project: Learn how yarn weights (#0 to #7) and fiber blends pair with your hooks.
• 🛋️ Evermore Plaid Granny Square Blanket Pattern (5.5 mm I-9 Hook): Put your 5.5 mm (I-9) hook to work with our cozy free plaid blanket pattern!