B-1 Crochet Hook (2.25 mm): Yarn Weight, Gauge and Size Conversions
The B-1 hook is 2.25 mm, old UK size 13. It suits super fine (fingering) yarn, which CYC gauges at 21 to 32 single crochet per 4 inches. At about 32 stitches per 4 inches, a 50 inch blanket starts with about 401 chains. A 20 inch hat band is about 160 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 2.25 mm, about 0.09 inch across. The US label B-1 and the 2.25 mm size describe the same hook, and old UK charts call it size 13. Letters vary between brands, so the millimeter size is the one to match.
What is the B-1 hook in mm and UK sizes?
| Metric | 2.25 mm |
|---|---|
| Inches (shank diameter) | 0.09 in |
| US letter and number | B-1 |
| Old UK size | 13 |
| Knitting needle, same diameter | US 1 (2.25 mm) |
| Usual yarn weight | super fine (fingering) |
| Estimated gauge | about 32 single crochet per 4 in |
What yarn weight do you use with a 2.25 mm crochet hook?
The Craft Yarn Council lists 2.25 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 |
|---|---|---|---|---|
| Super fine (fingering) | 2.25 to 3.5 mm (B-1 to E-4) | 21 to 32 | 264 to 401 | 105 to 160 |
What is the crochet chain length for a blanket with a B-1 hook?
The estimated gauge places 2.25 mm within the CYC hook range for super fine (fingering) yarn, giving about 32 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 241 |
| Receiving | 30 | about 241 |
| Baby / Crib | 42 | about 337 |
| Throw / Afghan | 50 | about 401 |
| Twin | 66 | about 529 |
| Full / Double | 80 | about 641 |
| Queen | 90 | about 721 |
| King | 108 | about 865 |
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 B-1 hook
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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Clover Quick Locking Stitch Marker Set
$12.96Locking markers that clip into a crochet loop or knit stitch to mark rounds and repeats.
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OttLite 4-Inch Hands-Free LED Magnifier
$23.99A 4.33 inch lens that hangs from a neck cord, so both hands stay free for fine stitches.
Check pricePrices change often, so confirm on Amazon. As an Amazon Associate we earn from qualifying purchases.
What knitting needle size matches a B-1 hook?
A US 1 knitting needle is also 2.25 mm. For the same yarn, though, CYC pairs super fine (fingering) with 2.25 to 3.5 mm (B-1 to E-4) hooks, which run larger than the matching needles because crochet fabric is denser.
What are the crochet hook sizes next to the B-1 hook?
Frequently asked questions
What size is a B-1 hook in mm?
The B-1 hook is 2.25 mm across the shank, about 0.09 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 nearest size on the chart is 2.5 mm.
What yarn weight do you use with a 2.25 mm crochet hook?
CYC places 2.25 mm within the recommended hook range for super fine (fingering) yarn. Super fine (fingering) is the usual match, with a hook range of 2.25 to 3.5 mm (B-1 to E-4) and a gauge of 21 to 32 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 B-1 hook?
At about 32 single crochet per 4 inches, our estimate for super fine (fingering) yarn on a 2.25 mm hook, a 50 inch wide throw starts with about 401 chains, including 1 turning chain. A 42 inch baby blanket needs about 337 and a 90 inch queen about 721. Foundation chains tend to be tighter than the rows above, so many crocheters chain with a hook one size larger.
What is a B-1 hook in UK sizes?
The old UK size is 13. 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 2.25 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 B-1 hook?
A US 1 knitting needle is also 2.25 mm. Same diameter does not mean same yarn: CYC pairs super fine (fingering) yarn with 2.25 to 3.5 mm (B-1 to E-4) hooks but 2.25 to 3.25 mm (US 1 to 3) needles, because crochet stitches are denser. For the same yarn, crocheters usually reach for a bigger tool than knitters.
Is a B-1 hook good for beginners?
It is better once you are comfortable with the basic stitches. At 2.25 mm the stitches are small, about 32 per 4 inches, so counting takes good light and patience. Thin hooks also encourage a tight grip, so a cushioned handle, bright daylight lamp and regular breaks help. Many beginners start on a 5 mm H-8 hook with worsted yarn.
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.