How crochet hooks and knitting needles are measured for size

This might be something that is blatantly obvious to everyone else but me, but recently I found myself wondering exactly HOW are crochet hooks and knitting needles measured for size?

Hooks and needles are usually presented with their sizes given in millimeters (for example, a 5.5 mm crochet hook or a set of 7 mm knitting needles). But do those millimeters represent the hook's/needle's CIRCUMFERENCE or DIAMETER???

This issue actually came up when I was working the Harmony Shawl free pattern while camping. I didn't pack all my yarncrafting supplies for the trip, but I had a white plastic 6.5 mm K hook on hand. The pattern actually recommends an 8 mm L hook to create a fabric with a relatively large gauge, however, so I improvised by working each stitch way up on the handle of my K hook, at the point where the handle flattens out and gets wider (see photo below).

Working stitch up on the flattened hilt of a K hook to achieve a larger gauge.

But because I was camping without all of my supplies, I had no way to measure just how big of a stitch I was approximating by working them up on the hilt of my K hook. And then I realized that even if I'd had a measuring tape on hand, I actually didn't know whether the hook's size represented its circumference or its diameter. D'oh!

After we returned home, I searched the Internet for information about how crochet hooks and knitting needles are measured. This Wikipedia article had some interesting information, but it didn't fully answer my question because its statement "Hooks come in various sizes (measured in millimetres or fractions of an inch), according to the thickness of the needle" didn't clarify what it meant by "thickness of the needle." One could still interpret that as either the circumference OR the diameter! ARGH!

So, finally, I pulled out my measuring tape and an I hook (5.5 mm size) and tested the measurements out for myself. As best as I could tell, its circumference measured at 19 mm! That's obviously WAY more millimeters than 5.5!

Next I measured the hook's diameter, and as you can see in the photo below, it's fairly close to 5.5 millimeters.

So, at last, I have my answer for how hooks and needles get their size rating, and in the process, I learned something new. Now I won't have to take those size markings for granted anymore!

And if you've ever wondered the same thing about hook and needle sizes, I hope this post helped you as well. Happy yarncrafting!

P.S. And in case you're wondering what crochet hook size I actually was approximating by working up on the hilt of my K hook, according to the diameter sizing rule, as far as I can tell, that spot on the hook measures at about 10 mm, which is the equivalent of a size N hook.

Getting mathematical with hats

I recently made the Brain Waves Beanie by Liz McQueen.

When reading her pattern, I found it interesting the way she included measurements for the diameter of the top of the hat at the end of each increasing round. (Most hat patterns only include the number of stitches you should have at the end of the round.)

Information about the diameter is important because when you stop increasing the size of the circle, that measurement will determine the circumference of the hat when you multiply it by Pi (as we learned in school with our friendly geometric formula: Pi times Diameter equals Circumference). And the circumference should correspond to the size of the head on the person you're making the hat for. Therefore, if the diameter of the top of the hat is about 7 inches across, then the finished hat will be about 22 inches around, because 7 times 3.14 equals 22 (in round numbers).

Alternatively, if you know the person's head circumference and want to determine your pattern from that measurement, the formula to tell you how large the diameter should be is Circumference divided by Pi. Therefore, if you want your hat to have a finished circumference of 22 inches, then 22 divided by 3.14 equals a diameter of about 7 inches.

This disc measures about 6.5 inches across (when laid flat; the edges are trying to curl in the photo), so that means if I stop increasing here, the finished hat will be about 20.5 inches.

Each round of (in this case) double crochet worked with a J hook using worsted-weight yarn is about .5 inches high, which means that each successive round adds about 1 inch to the diameter of the circle. If I add another increasing round to what I have in the photo (making the diameter about 7.5 inches), the finished hat circumference will be 23.5 inches. (A bit on the large size for most folks.)

Alternatively, if I made the same hat top using half-double crochet, the diameter size would be proportionally smaller.

When you factor in the differences in height that the various stitches have, plus how those stitches are affected by the weight of the yarn and the size of your hook, the potential combinations can be mind-boggling. Which is probably why pattern designers emphasize the importance of always working a test swatch before attempting a pattern.