It there a rule of thumb for how long yarn should be to complete a row of stickinette - like 4 times the lenght of the knitted piece? I'm trying to only attach new balls at the end of rows.
I think it's about 2x the length of the piece. When I do stockinette stitch, I join even in the middle of the piece. The ends can be tucked into the purl bumps anywhere and they don't show on the front.
It's usually more then twice the width of the piece and less then 4 times the width of the piece....but closer then that you need to swatch.
MMario - I'm not divorced from reality - we're having a trial separation
There is no one rule that will apply, since you may be using different sizes of needles, and your own personal tension, plus the kind of patterning you are using. Sorry....
The best thing to do is just measure how much yarn YOU use in a row/round with that particular yarn and those needles, and that stitch pattern. I measure off an arm's length or a metre or a yard -- whatever you want, and see how far it goes. Do this anytime you are nearing the end of a ball, and that will give you the best guesstimate of how much yarn you will need for one row or round.
I have generally allowed about 3 times the length of a round, but I find there is always a couple of inches to spare. Better to have more than not enough!!
My general rule is about three times the length of the row/round, but that's only if I'm using the typical size needle for the yarn weight. It also depends on your particular tension. No easy answer! When in doubt..swatch (for some reason, that's my last resort).