It may seem obvious, but accurate measurements are critical. Those of you who have been on the List for a while may remember that about a year and a half ago, when the Sock Craze first started, I asked the List to "go stand on a ruler" in an effort to compile a chart of shoe sizes to their corresponding inches of foot (so to speak! <bg>). I was amazed at the variation in foot length that was reported for the same shoe size. I'm still not sure if this is due to different measurement techniques (I refuse to believe that *knitters* could measure anything incorrectly!!), or due to the fact that the same shoe size really will fit feet of such different dimensions (for instance, shorter but wider will fit into the same shoe as longer but thinner).
For an ankle length sock, the measurements needed are:
1. Circumference of ankle, just above the ankle bone
2. Length of foot (best measured, quite literally, by standing on a ruler; the length is from where the heel lies on the ruler to the tip of the longest toe, which may or may not be the big toe).
3. Height of heel from floor to ankle bone (the bottom of it!).
These measurements tell you:
1. How many stitches you need to get around the ankle - gauge times ankle circumference minus about 20 percent for stretch and stay-upness.
2. How long the foot needs to be (measure the sock from the point of the heel-turn; when you're about two or two and a half inches short of the foot length, start the toe. Here again, you want to be a *little* short so the sock can stretch to fit without being floppy and too loose.)
3. How deep the heel flap needs to be. This is a tricky one. Standard heel flap heights 2.5" for women, 3" for men. If, however, you find that the sock fits okay once it's on but is a real struggle to get your foot into, then you need to make the heel flap deeper. And, once again, I always knit this dimension *slightly* small to allow for stretch. (Can you tell I like a *fitted* sock? <bg>) Gusset pick-up stitches depend heavily upon heel flap length, and do *not*not*not* equal the number of slip stitch rows, as I pointed out in my pattern but as many patterns insist they do. If your gusset stitches equal your slip stitch rows in the heel flap, you will have Dreaded Gusset Hole syndrome, plain and simple. You should have one or two more stitches in the gusset pick-up than you had slip stitch rows in the heel flap. It makes *no* difference to the fit of the sock - you're still going to decrease them away till you have the number of stitches that you had at the ankle.
As you may have noticed in my sock pattern, I cast on four extra stitches for the ribbed cuff, which I then decrease away as I go down the ankle. My ankle measures a bit less than 8.5"; at 8 sts/inch, less 20% stretch, I come up with 53 sts, which I round down to 52 for the ankle (that's using 8.3" for the ankle measurement, in case you want to check the accuracy of my calculator!). Like most people, my calf is fatter than my ankle, which is why I use the extra four stitches in the ribbing.
When you get into taller socks, things get even more interesting. Boot socks or calf high are a real problem to get to stay up, since you're dealing with the top of the sock equaling the fattest dimension of the calf. I've knitted boot socks for my uncle, and I generally do them in all ribbing all the way down the leg, with just an inch or so of stockinette before the heel, if any.
So your measurement to add to the above List of Three for boot/calf-high socks is the calf measurement where you want the top of the sock to hit. Then you fit your ribbing to that measurement less 20 percent for stretch. Now, you'll need to make sure you decrease above the ankle, after you switch from ribbing to stockinette, to get your stitches to match your ankle measurement (this is similar to what I did in the pattern where four sts. got decreased away down the center back). You need to do this not only to make the sock fit around the ankle, but also to make the foot fit properly since you typically use the same number of stitches in the foot as for the ankle.
Alternatively, if you don't want to switch to stockinette or you don't want to decrease at the ankle, you can simply do extra gusset decreases to get down to the ankle-measurement-times-gauge-less-twenty-percent number. Remember that if you do this, you'll need fewer rows between gusset end and toe start since you've got extra rows in the gusset.
Knee socks - these are fun, though they're a lot more work (I consider them almost equivalent to a pair of sleeves!). Here, you add two more measurements to the List of Three: (4) circumference of leg below knee (where the sock top will hit) and (5) circumference of the fattest part of the calf.
Knee socks lend themselves beautifully to fancy turnover cuffs - lace, cables, colourwork - such as those found in Lady Gainsborough's _Kilt_Hose_ book (wonderful book!). Cuff stitches are calculated based on the #4 measurement and the number of stitches needed for the pattern in question; the cuff does *not* have to fit snugly, though it shouldn't, of course, balloon out. Once the cuff is completed, knit a turning row (such as a row of purl on the right side), then adjust the number of stitches to fit the #4 measurement. Knit a k1, p1 "garter" that is slightly shorter than the cuff length. This, hopefully, will help your knee sock stay up. Then TURN THE SOCK INSIDE OUT! since the cuff folds over, or your sock leg will be inside out in relation to the cuff! ;)
Knit down the leg, using whatever pattern stitch interests you (cables along the sides, etc.). As you proceed, you will need to gradually INCREASE (typically along the center back "seam") to adjust the sock to the #5 measurement (fattest part of calf - remembering to reduce about 20% for stretch and stay-upness). Then, of course, you will need to start DECREASING down the center back as you proceed from the calf on down to the ankle. Heel and foot are done as usual.
All of this is described in the _Kilt_Hose_ book.
Putting fancy patterns along the side of the sock can be done with socks of any length. The trick is to adjust the pattern so that it falls just in *front* of the heel, if you want it to continue down the sides of the foot. Therefore, if you have, for example, a 4-stitch fancy pattern to go on each side of the leg and then on down the foot, and the sock is the one for which I gave the pattern with 52 ankle stitches, the pattern has to fall after the first 16 stitches of the row and before the last 16 stitches, assuming it starts before the decreasing down from 56 stitches. Clear as mud? Well, you have 26 instep stitches, right? and you have also got 26 heel stitches. But at the beginning, there are four extra stitches that get decreased away. Add those four into the heel stitches, since they technically belong to the back part of the sock (they get decreased away at center back). That gives you 30 stitches for the back half of the sock. Then take one more stitch away from the front and put it on the back - that stitch will be between the pattern and the gusset. So. 32 stitches for the back half, divided by two, is 16 stitches for each side. Which gives us: 16 sts for first side of back half 4 sts for the pattern (from the instep) 16 sts for the rest of the instep 4 sts for the pattern (from the instep) 16 sts for the other side of the back half adds up to the 56 stitches that we cast on. Once we decrease away the extra four stitches, we have: 14 sts, first side back half 4 sts pattern 16 sts instep 4 sts pattern 14 sts, second side back half adds up to 52 sts, and we have 26 (14 + 14 are the two back halves) sts to turn the heel plus two extra, one each side for the gusset decrease line.