J-10 Crochet Hook (6 mm): Yarn Weight, Gauge and Size Conversions
The J-10 hook is 6 mm, old UK size 4. It suits medium (worsted) yarn, which CYC gauges at 11 to 14 single crochet per 4 inches. At about 12.5 stitches per 4 inches, a 50 inch blanket starts with about 157 chains. A 20 inch hat band is about 63 stitches around.
Crochet hook size is the diameter of the shank, the smooth part of the hook that sets the size of each loop. This hook is 6 mm, about 0.24 inch across. The US label J-10 and the 6 mm size describe the same hook, and old UK charts call it size 4. Letters vary between brands, so the millimeter size is the one to match.
What is the J-10 hook in mm and UK sizes?
| Metric | 6 mm |
|---|---|
| Inches (shank diameter) | 0.24 in |
| US letter and number | J-10 |
| Old UK size | 4 |
| Knitting needle, same diameter | US 10 (6 mm) |
| Usual yarn weight | medium (worsted) |
| Estimated gauge | about 12.5 single crochet per 4 in |
Charts also list the sizes below. They are close enough to 6 mm, or labeled so inconsistently between brands, that they share this page.
| Metric | US | Old UK | Note |
|---|---|---|---|
| 5.75 mm | J | None | Less common; listed on the CYC chart. |
What yarn weight do you use with a 6 mm crochet hook?
The Craft Yarn Council lists 6 mm inside the recommended hook range for the weights below. The chain and hat columns show how far the full gauge range of each weight moves the stitch count.
| Yarn weight | CYC hook range | Single crochet per 4 in | Chain for 50 in | 20 in hat band |
|---|---|---|---|---|
| Medium (worsted) | 5.5 to 6.5 mm (I-9 to K-10.5) | 11 to 14 | 139 to 176 | 55 to 70 |
What is the crochet chain length for a blanket with a J-10 hook?
The estimated gauge places 6 mm within the CYC hook range for medium (worsted) yarn, giving about 12.5 single crochet per 4 inches. Each starting chain is the stitches needed for the width plus 1 turning chain for single crochet. Rows of taller stitches or lacy patterns change the width per stitch, so swatch in the stitch you plan to use.
| Blanket | Width (in) | Starting chain (estimate) |
|---|---|---|
| Stroller / Car Seat | 30 | about 95 |
| Receiving | 30 | about 95 |
| Baby / Crib | 42 | about 132 |
| Throw / Afghan | 50 | about 157 |
| Twin | 66 | about 207 |
| Full / Double | 80 | about 251 |
| Queen | 90 | about 282 |
| King | 108 | about 339 |
Chain loosely, or go up a size
Foundation chains are usually tighter than the rows above them, which makes the bottom edge pull in. Many crocheters chain with a hook one size larger, then switch back. Enter your own swatch in the crochet chain calculator for an exact count.
Hooks and supplies for a J-10 hook
Prym Ergonomic Crochet Hook Set, 5 pieces
$24.35Five rubberized ergonomic hooks in 3.5, 4, 4.5, 5 and 6 mm.
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Clover Amour Crochet Hook Set 3674, 2 to 6 mm
$90.22Clover Amour soft grip hooks in every half millimeter from 2 to 6 mm.
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Boye Aluminum Crochet Hook Set, US D to K
$16.79Eight color-coded aluminum hooks from 3.125 to 6.5 mm, an inexpensive way to own every common size.
Check pricePrices change often, so confirm on Amazon. As an Amazon Associate we earn from qualifying purchases.
What knitting needle size matches a J-10 hook?
A US 10 knitting needle is also 6 mm. For the same yarn, though, CYC pairs medium (worsted) with 5.5 to 6.5 mm (I-9 to K-10.5) hooks, which run larger than the matching needles because crochet fabric is denser.
What are the crochet hook sizes next to the J-10 hook?
Frequently asked questions
What size is a J-10 hook in mm?
The J-10 hook is 6 mm across the shank, about 0.24 inch. Charts also list 5.75 mm (J), covered on this page. Letters and numbers vary between brands, especially at the large end, so the millimeter size stamped on the hook is the one to trust. The neighboring sizes are I-9 (5.5 mm) and K-10.5 (6.5 mm).
What yarn weight do you use with a 6 mm crochet hook?
CYC places 6 mm within the recommended hook range for medium (worsted) yarn. Medium (worsted) is the usual match, with a hook range of 5.5 to 6.5 mm (I-9 to K-10.5) and a gauge of 11 to 14 single crochet per 4 inches. It sits inside one category, so it is a straightforward match. Amigurumi often uses a smaller hook than the label for tight stitches.
How many chains do I need for a blanket with a J-10 hook?
At about 12.5 single crochet per 4 inches, our estimate for medium (worsted) yarn on a 6 mm hook, a 50 inch wide throw starts with about 157 chains, including 1 turning chain. A 42 inch baby blanket needs about 132 and a 90 inch queen about 282. Foundation chains tend to be tighter than the rows above, so many crocheters chain with a hook one size larger.
What is a J-10 hook in UK sizes?
The old UK size is 4. Old UK numbers run in reverse, so higher numbers are finer hooks. Current UK and European patterns use millimeters, so a pattern asking for a 6 mm hook means this exact size. Watch the stitch names as well as the hook: UK double crochet is the same stitch as US single crochet, and UK treble is US double crochet.
What knitting needle is the same size as a J-10 hook?
A US 10 knitting needle is also 6 mm. Same diameter does not mean same yarn: CYC pairs medium (worsted) yarn with 5.5 to 6.5 mm (I-9 to K-10.5) hooks but 4.5 to 5.5 mm (US 7 to 9) needles, because crochet stitches are denser. For the same yarn, crocheters usually reach for a bigger tool than knitters.
Is a J-10 hook good for beginners?
Yes. A 6 mm hook with medium (worsted) yarn is a size many beginner guides suggest, because stitches are big enough to see and count. A 20 inch hat band is only about 63 stitches, and mistakes are easy to pull out. Choose a smooth, light-colored yarn so you can see each loop, and try a cushioned handle if your hand tires.
How we research: we compare manufacturer specifications, owner manuals, published standards and recurring themes in verified owner reviews. We do not test products in person, and this is researched guidance, not professional advice. Follow your machine manual and pattern, and take care with rotary cutters, hot irons and needles. As an Amazon Associate we earn from qualifying purchases.