Well, I Did Warn You...
Hats are the easiest. Key concepts to keep in mind are the style of hat that you want and how stretchy your stitch pattern is in each direction. Converting the measurements directly into a hat pattern gets you a slightly loose short beanie. If you want it to fit snugly, pull the number of stitches down a little bit. If you want a watch cap, make it longer. If you want a snood-like hat or a beret, you will need increases and decreases, so that the hat can fit tightly at the band, but loosely above it. You can also design the hat to be knitted from the brim up or from the top down. For a watch cap, this is how I do it:
- Decide if it will be made top-down or brim up. This determines whether I will be using increases or decreases for the crown shaping. I usually do brim-up, because my cast-ons look a lot better than my binding off.
- Convert measurements into stitches and rows, rounding down to a multiple of 5 (or other number if you prefer, 4-8 all work, with some tweaking). If the stitch pattern is particularly stretchy, I might reduce the stitches considerably so I don't end up with a super-loose hat. The concept to keep in mind is "how big will this be when stretched to normal wearing tension?"
- Work out the crown shaping. Remembering that the row measurement is ear-to-ear, divide it by 2. You have about this many rows, total, to do your crown shaping. You usually won't need that many. You will always want to do decreases on the last (or increases on the first) 3 rows or so to avoid a "nipple" shape at the top of the hat. In a hat that uses multiples of 5, that means the last 3 rows will have 15 stitches, 10 stitches, and 5 stitches, respectively.
What remains is to get rid of all the other stitches, down to 15. Subtract 15 from the total number of stitches in the hat, then divide by 5 (adjust accordingly if you used something other than 5 as your base). This is the number of decrease rows you will need. If you want to make the hat easiest to make, just alternate decrease rows and plain rows until you have worked this many, ending with a plain row with 15 stitches in it. If you want your hat to have a more graceful transition from vertical to top, divide your decrease rows in half, and work every third row as a decrease for the first half, then every row, then your 3 final rows. - Work out the length. The measurements taken give you a beanie. Simply decide how much extra length you want, convert it to rows, and tack it on. This is the time to round your length off to a pattern repeat if you are using one- it is most common to work the entire portion before the decreases in pattern, then go to something simpler or just straight stockinette for the crown so that the decreases are easier to work.
- Knit! If you weren't sure about your circumference, you can check it about two inches into the knitting. By then, it should stretch out to about the same degree it will when worn. Before that, it will be extra-stretchy, and might not bounce back, so stretching it out to test can leave you with a floppy edge on an otherwise perfect hat.
- Decide if you are working toe-up or cuff-down. Most knitters are fiercely for one or the other. Personally, I'm a toe-up girl. Makes me happy to be able to try it on and know how it feels from the toes up, and I like the idea of being able to cut it close on yarn without making toeless socks.
- Decide which toe and heel you are using. Simplest to design is short-row toe and heel, both identical, but many people prefer other methods, especially a heel flap. Most methods will have you either work a gusset to add stitches for the heel or have you work some kind of cup over more than half the stitches. Toes are usually a bit simpler.
- Convert your measurements into stitches and rows. Socks are usually slightly smaller in circumference and length than the actual foot, and significantly smaller in circumference than the leg. The amount of negative ease you will want will depend on the structure of the fabric you plan to make (ribbed, flat, lace, etc.), its thickness, and how tight you like your socks.
- Determine how long your toe shaping is. It will take a certain number of rows to go from full circumference to something bind-off-able (or the equivalent). The most common rule of thumb I have seen is 1/4 the length of the foot. My personal rule of thumb is to try to arrange it so that it is done before widest part of the ball of the foot, and I design down from the full circumference rather than up from the number I want at the tip of the toes.
- Determine how long your heel shaping is. Again, I have seen 1/4 the foot length offered as a rule of thumb. Depending on your particular heel shaping style, measurement 5 could come in very handy here. If you are making a gusset, you might need to start it earlier than the "elbow", however.
- Determine how much foot length that leaves. This is the bit of the foot you will get to knit plain (or in pattern with no shaping).
- Determine how long the leg part of the sock should be, and how much of it should be ribbing (if any). Pretty simple, really. You can either measure from the floor and subtract the vertical length of the heel shaping you already added, or just measure from the top of the heel shaping.
- Determine circumference of sock leg. If you are making a crew sock or shorter, this can be a constant as long as the pattern is stretchy. If you are making a sock that covers the calf or knee, you will need to add some increases and decreases or risk making the leg look like a sausage.
- Add shaping if necessary or desired. Determine the difference between two measurements- for example, the circumference of the sock at the ankle and the circumference at the widest part of the calf. Divide the difference in stitch counts by the number of rows. You will need to increase every this many rows (or so). It rarely comes out even, so you will probably need to adjust somehow.
Example: I want to go from 50 stitches at the ankle to 70 stitches at the calf. The two measurements are 50 rows apart. 70-50=20 stitches difference, and 50/20=2.5 rows between increase. It's impossible for me to work an increase on a half row, so I can either achieve this by working 2 increases every 5th row, or work my increases at uneven intervals- 2 rows, then 3 rows, 2, 3, and so on.
Decreases work the same way, just in the other direction. The only place you are likely to need decreases is above the calf, so that the sock doesn't bag at the knee.