Hook sizes: the letter, the millimetre and the old UK number
My hooks live in a jam jar, and half of them have the letter worn off. This is the chart that tells you what the letter meant, what it is in millimetres and in UK sizes, and when to go up or down one for a square that will not lie flat.
A hook is measured by the diameter of its shaft in millimetres, and that is the only number on it that means the same thing everywhere. They run from 0.6mm, which is a steel thing for thread, up to 25mm, which is more of a broom handle. Two sizes do most of the work on this porch: 5mm, the one stamped H or 8, for worsted, and 4mm, stamped G or 6, for DK. Patterns tend to print the letter and the millimetre together; when they disagree with each other, the millimetre is the one telling the truth. Then two adjustments worth learning by heart: go down half a millimetre when the piece will be stuffed and you want the fabric closed, and go up half a millimetre when you want a blanket to fall rather than stand.
| Millimetres | US letter | Old UK | Yarn it suits | Where it earns its keep |
|---|---|---|---|---|
| 2.25mm | B/1 | 13 | Lace / thread | Doilies and fine lace |
| 2.75mm | C/2 | 12 | Lace / sock | Small motifs worked close |
| 3.25mm | D/3 | 10 | Sock / fingering | Shawls, socks, fine work |
| 3.5mm | E/4 | 9 | Sport / DK | Baby things; the smallest toys |
| 3.75mm | F/5 | 9 | DK / light worsted | DK squares with a bit of give |
| 4mm | G/6 | 8 | DK / light worsted | The DK default |
| 4.5mm | 7 | 7 | DK / worsted | Worsted, worked tight on purpose |
| 5mm | H/8 | 6 | Worsted | The one that is never in the jar |
| 5.5mm | I/9 | 5 | Worsted / aran | Aran, or worsted with more drape |
| 6mm | J/10 | 4 | Aran / bulky | Heavy squares, throws |
| 6.5mm | K/10½ | 3 | Bulky | A blanket in a fortnight |
| 8mm | L/11 | 0 | Super bulky | Baskets that stand up on their own |
| 9mm | M/13 | 00 | Super bulky | Big, soft, quick |
| 10mm | N/15 | 000 | Jumbo / roving | Rugs and floor cushions |
| 15mm+ | P/Q/S | — | Jumbo | Arm work. Both hands, no subtlety |
Picking one out of the jar
Two sources of truth, and a rule for the evenings they disagree.
Start with the band, then read the pattern
Start from the ball band, because the size printed there is what the mill actually tested that yarn against. Then read the pattern, which is one person's tension on one afternoon and may be firmer or looser than the mill's. If those two agree, take the hook and get on with it.
When the two of them disagree
When they disagree, or when the pattern is silent, ask what the fabric has to do. Something that gets stuffed needs to close up, so take the hook down half a millimetre from the band and accept that your hand will work a little harder. Something meant to hang — a blanket over the arm of a chair, a light wrap — wants the hook up half a millimetre so the stitches can move against each other. That half-millimetre is the whole adjustment. There is rarely a reason to go further than one step in either direction without swatching first.
Going up a size, going down a size
A pattern names a hook, and that hook is the one the designer's hands wanted. Yours are not her hands. The number to trust is the gauge — the stitches and rows the pattern says you should get across four inches — and the hook is only how you arrive at it. Work the square the pattern opens with, lay a ruler across it, and compare.
Too many stitches in four inches means your work is tighter than hers: go up half a millimetre and try again. Too few means it is looser: go down. Half a millimetre is a real step and usually enough; a whole millimetre changes the fabric as well as the size, which is sometimes what you want and never what you want by accident.
There is one place the pattern's hook is not a suggestion. Anything that will be stuffed wants a hook a size or two under what the ball band says, so the fabric closes and the stuffing stays behind it. On a stuffed toy a loose hook is not a different size, it is a visible mistake.
Why the letter lets you down and the millimetre does not
The US letters were never standardised across the trade. One maker's J is six millimetres and another's is six and a half, and both are stamped J, and neither of them is wrong exactly — they simply never agreed. A half millimetre sounds like nothing until it has run through forty rounds of a square, at which point it is a finished piece that will not join to the one you made last week.
So when you are buying, and especially when you are buying from a photograph on a screen or following a pattern written on the other side of the world, read the millimetre and ignore the letter. If the hook only carries a letter, put a caliper on it once and write the number on a bit of tape round the handle. Mine are all labelled that way, which is why the worn letters stopped mattering.
Asked on the porch
I have never held one. Which size do I buy?
A 5mm, stamped H or 8, with a worsted yarn. Stitches at that size are large enough to see, and worsted forgives a lot of uneven tension while you are finding it.
What hook do stuffed toys want?
Usually 4mm or 4.5mm with worsted yarn — a half size or a whole size smaller than that yarn would normally take. The point is a fabric with no gaps in it, so the stuffing stays inside and the shape holds.
The pattern says H and my hook says a number
Five millimetres. You will also see it stamped H/8.
I have a 4mm hook — what letter is that?
G, or G/6 on a hook that carries both.
Do I go up a size or down a size?
Down when the piece is stuffed or needs to hold its own shape. Up when you want it to drape. Half a millimetre at a time, and work a square and measure it before you make forty more.
Are all brands' hooks the same size?
The millimetres are. The letters are not — one maker's J can be 6mm and another's 6.5mm. Trust the number, not the letter.
Aluminium, wood, and the handle question
Plain aluminium is what most of the jar is: cheap, hard-wearing, and slick enough that the yarn does not drag. Bamboo and wood are warmer to hold and grip a little more, which is a help with slippery cotton and a hindrance with anything that already sticks. Neither one changes your gauge on its own; the size does that.
The one upgrade worth spending money on is a fat cushioned handle, and I say that as somebody who resisted it for years. If you are crocheting most evenings, or if your hands ache by the third round, a padded grip is not an indulgence. Buy one in the size you use most — for the majority of us that is the 5mm — and see how the week goes before replacing the rest.