Hats in many sizes and gauges

	12	14	16	18	20	22	24
16	44	48	56	64	72	76	84
17	44	52	60	68	76	84	88
18	48	56	64	72	80	88	96
19	52	56	68	76	84	92	100
20	52	60	72	80	88	96	108
21	56	64	72	84	92	100	112
22	60	68	76	88	96	108	116
23	60	72	80	92	100	112	124
24	64	72	84	96	108	116	128

What is this table all about? It will help you find the right number to cast on when making a hat. Red numbers on the left are different head circumferences in inches. Pick the one you need and mark the row. Blue numbers on a top are gauge per 4". Pick one you have, and mark the column. Required number to cast on will be the one where marked row and column cross. If you had head circumference of 21" and gauge of 24sts/4", you would have to cast on 112 stitches.

Now we know the number to cast on. What now?

Cast on required number of stitches. Place marker. Join the round, being careful not to twist. Knit in 2x2 rib for 5 rounds. After that, knit in stockinette stitch until the hat is high enough. How will you know the hat is high enough? Try it on a person, and see does it almost reach the top of the head. If you don't have the receipient handy, don't stress. Since it has ribbed brim, it can be folded. For a grown up man I usually knit untill I have 6" from the edge, and for a grown up women, 5-5.5" is enough. After that, start decreasing.

Each number of CO stitches will have its own decrease rounds, but the pattern is still work in progress, so here are some of the numbers:

44:
R1: *(k2, k2tog)*
R2 k
R3: *(k1, k2tog)*
R: k
R5: *(k2tog)*
R6 k1, *(k2tog)*
Thread yarn through remaining stitches and pull tight.

56, 64, 72, 80:
R 1: (k2tog, k6)*
R 2: k*
R 3: (k2tog, k5)*
R 4: k*
R 5: (k2tog, k4)*
R 6: k*
R 7: (k2tog, k3)*
R 8: k*
R 9: (k2tog, k2)*
R 10: k*
R 11: (k2tog, k1)*
R 12: k*
R 13: k2tog*
Thread yarn through remaining stitches and pull tight.

88, 96, 104, 112, 120, 128:
R 1: (k2tog, k6)*
R 2: k*
R 3: (k2tog, k5)*
R 4: k*
R 5: (k2tog, k4)*
R 6: k*
R 7: (k2tog, k3)*
R 8: k*
R 9: (k2tog, k2)*
R 10: k*
R 11: (k2tog, k1)*
R 12: k*
R 13: k2tog*
R14: k2tog*
Thread yarn through remaining stitches and pull tight.

Of course, knitting hats is not exact science. Every knitter's gauge differs, so does row gauge for every yarn. If you think you will have hat too high, just omit all knit rounds, and do decreases every row.

I'll add decrease rounds for other numbers when i'll be less sleepy:)