This four-pair mitten project was my first real game of yarn chicken. And, depending on how you look at it, either I lost or I won only due to creative rewriting of the rules. I started with 1 ounce each of four colors. I wound them into two, hopefully-matching 1/2-ounce balls (which I measured out on the kitchen scale) to spread evenly over the pairs of mittens. I did not swatch or even do any math to be sure that I actually had enough yarn for the pattern; I just dove into knitting.
My mittens are all supposed to be bi-color. One color was for the cuff and thumb, the other color was the hand. But look closely at this picture, and you can see that one set of mittens has three colors - the thumb does not match the cuff. Apparently the brown yarn was a smidge heavier for its length than the other colors, and ran out sooner. The pile of yarn in the center of the picture is everything I had left at the end, including trimmings and nerdles.