So how do I do it? Weighing squares for my sock yarn blankie. I started in March, using only washable, fingering weight yarn that was leftover from previous projects. They don't have to be socks, because I use that weight yarn for lots of things, but they definitely have to be leftovers.
I'm including the yardage in my 2009 12 mile quest instead of saving them for whenever the blanket is finished because it would totally skew that year. In other words;
Knit Picks Essential: 619 yds
Knit Picks Imagination: 70 yds
Knit Picks Gloss: 70 yds
Mountain Colors Bearfoot: 154 yds
Koigu KPPPM: 202 yds
Plymouth Happy Feet: 58 yds