Is there a standard ratio of reducing? I'm knitting in round up and wonder if it's every row or every other
I do every other row. If you are working from the bottom up, you have a huge swatch to measure the row gauge. From this you can figure out how to do your reducing to make the yoke the depth you want. I usually go for l0 or ll inches but you could measure a sweater that is comfortable on you.
how deep does the armhole for the raglan sleeve need to be? If it needs to be 8 inches deep let's say, and your row gauge is 7 rows per inch, then you have the fundamental information you need to calculate the number of rounds between each decrease round. Suppose you need to decrease from 120 stitches to 80. That's 40 stitches that need to be decreased within 8 inches (my math is completely made up and has no validity as to fit by the way). Assuming you're doing a double decrease at the front and back of the sleeve, then you will decrease 4 stitches per sleeve on the decrease round. That means you need to have 10 decrease rounds (40 decreased stitches divided by 4 stitches per decrease round). If you want to achieve this within an 8 inch depth at the armhole, then you will have 56 rounds in which to do this(8 inches times a row gauge of 7 rounds per inch). Take the number of rounds for the armhole depth (56 rounds) and divide it by the number of decrease rounds minus 1 (10-1=9), and divide this into 56 and you get roughly 6, so you would need to decrease every 6th round.
Hope this helps.