M/N-13 Crochet Hook (9 mm): Yarn Weight, Gauge and Size Conversions

The M/N-13 hook is 9 mm across the shank, about 0.35 inch. Hook size is measured on the shank, the smooth section between the throat and the thumb rest, because that part sets the size of every loop. 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 L-11 (8 mm) and N/P-15 (10 mm).

CYC places 9 mm within the recommended hook range for bulky (chunky) and super bulky yarn. Super bulky is the usual match, with a hook range of 9 to 15 mm (M-13 to Q) and a gauge of 7 to 9 single crochet per 4 inches. Sitting where two categories meet, it gives the lighter yarn a looser, drapier fabric and the heavier yarn a firmer one. With chunky yarn, start from the hook printed on the label, because thickness varies between brands.

At about 9 single crochet per 4 inches, our estimate for super bulky yarn on a 9 mm hook, a 50 inch wide throw starts with about 114 chains, including 1 turning chain. A 42 inch baby blanket needs about 96 and a 90 inch queen about 204. Foundation chains tend to be tighter than the rows above, so many crocheters chain with a hook one size larger.

The old UK size is 00. 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 9 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.

A US 13 knitting needle is also 9 mm. Same diameter does not mean same yarn: CYC pairs super bulky yarn with 9 to 15 mm (M-13 to Q) hooks but 8 to 12.75 mm (US 11 to 17) needles, because crochet stitches are denser. For the same yarn, crocheters usually reach for a bigger tool than knitters.

For chunky projects, yes. A 9 mm hook works up fast: a 50 inch throw starts with only 114 chains, and stitches are easy to see. The catch is weight: bulky yarn and a big blanket in your lap get heavy, and large loops can be hard to read. A scarf or cowl makes a good first project at this size.

Work a swatch at least 6 inches square in the stitch the pattern names, lay it flat without stretching it, and count the stitches across the center 4 inches. On a 9 mm hook in super bulky yarn that is about 9 single crochet per 4 inches. Gauge is not a formality: the same 114 chain foundation worked 1 stitch per 4 inches tighter measures about 45.2 inches instead of 50, roughly 4.8 inches narrower. Feed your own swatch into the gauge calculator and it converts to a stitch count for any width.

For a worsted weight blanket, 5.5 to 6.5 mm (I-9 to K-10.5): a 50 inch wide throw starts with about 157 chains at 11 to 14 single crochet per 4 inches. On this 9 mm hook in super bulky yarn the same 50 inches is about 114 chains, so it works up far faster. The trade-off is weight and open stitches, so heavier yarn suits throws and lap blankets better than bed covers. The blanket yarn calculator gives the yarn for your own size.