To make a basic hat you will need approximately one 3 oz. skein of yarn, and a pair of circular needles and a set of double points in a size that corresponds with the yarn you have chosen.
Start by making a stockinette stitch sample. Measure your stitches to the inch. This number is “A” in the formula.
Decide how large around you would like your hat to be (about 20″ – 22″ for an adult head). Subtract 1″ from this for a loose fit, 2″ for a snug fit. This number is “B” in the formula.
Take “A” (your “stitches to an inch”) times “B” (your inches around minus1-2″). This gives you “C”. Add or subtract a little from “C” until it is divisible by 10*.
Add or subtract a little from “C” to make it divisible by 4. This is “D”.
The difference between “C” and “D” gives you “E”.
Cast on “D” stitches. Working in the round, do knit 2, purl 2 ribbing until the ribbing is desired length i.e. if the hat is to be worn with the ribbing folded up, make the ribbing long enough to be folded (about 6″ on an adult hat).
After the ribbing, working in stockinette stitch, increase or decrease “E” so that you have “C” stitches on the needle. Continue to work in stockinette until the hat, measured from cast on edge or fold of brim (depending on your design), measures 5 1/2″ for child’s size, 6″ for teen’s, 6 1/2″ for women’s, 7″ for men’s.
To decrease for top of hat*: (change to double points when necessary)
K8, k2tog around.
K two rnds even.
K7, k2tog around.
K two rnds even.
K6, k2tog around.
Continue in this manner. When you get down to around half of “D”, dec every rnd.
Last rnd: K2tog around. Break yarn. Draw through remaining stitches. Sew in ends.
*If your number of cast on stitches (“D”) is divisible by 9, start your decreases for the top of the hat with K7, k2tog…; if by 8, start the decreases with k6, k2 tog…; if by 7, start dec by k5…etc. NOTE: “D” also needs to be divisible by 4 for k2, p2 ribbing, or by 2 for k1, p1 ribbing. If necessary, cast on a stitch or two more or less than what is needed to make the top decreases work out, and increase or decrease to that number of stitches once you have knitted the ribbing.