I saw a "formula" on a Web site that was pretty helpful for adjusting patterns to a new stitch size.
Let's say your pattern calls for 30 st over 4".
Knit a swatch, and you have 19 st over 4", not 30.
So divide 19/30 = 0.63. That is your "multiplier." In other words, you need 63% of the number of stitches called for in the pattern to use the gauge in your swatch. 63% of 30 = 19. So if you are supposed to have 114 st/row as the pattern calls for, multiply that by .63 to get the adjusted number of stitches to use the gauge of your swatch (114 x .63 = about 72 stitches). So instead of a row that has 114 stitches, you have a row of 72 stitches to get the same size.
It works the same way for row gauge.
It gets a little trickier for armholes and necklines. I haven't tried that yet, but I imagine it's not that hard to figure out (famous last words....)
I saw a freeware program called Knitting Companion (I ***think*** that's the name) It's a simple thing, really geared towards machine knitting, but it works for hand knitting too. It tells you the adjustments in stitch and row numbers you need to make.
I'd rather be knitting