Hat formula!

Does anyone have an easy formula for hats? I need to be able to adjust the size of the hat with different size needles and yarn. Is there an easy math formula out there? Help!

I’ve made MANY and I’ve never heard of one. You have to make some to see if they meet the measurements you need. That also goes for needle size. Lots of manual labor.

if you already have a hat pettern, but the yarn and needles you have differ from those recomended, you will have to do a gauge swatch with your yarn.

cast on 20 stitches and knit a stockinette (alternate rows of knits and purls) square (you may want to do a small border of garter stitch, knit every row to prevent curling. measure 2 inches in the middle of the square and count how many stitches there are and how many rows there are. If you halve this you have the gauge in stitches per inch, if you double it you have stitches per 4 inches (both are commonly given).
Now compare that to the gauge stated in the pattern.

take the guage information from the pattern. number of cast on stitches/stitches per inch = final measuremtn of the hat.
put your gauge into this formula, does it give you the smae measurement? if it does the yarn will work if not then it needs a bit more maths.
final measurment x stitches per inch = number of cast on stitches.
e.g.the pattern tells you that 90 (cast on stitches) / 6 (stitches per inch) = 15 inch brim of hat

your gauge tells you 5 (stitches per inch) X 15 (the size of the hat) = 75 (cast on sticthes)

http://www.mielkesfarm.com/bsic_hat.htm

http://www.thedietdiary.com/knittingfiend/tools/knittingHat.html
Crown shaping calculator