SockCalc for iPhone is a handheld version of the Arachne Sock Calculator, a sock pattern generator. Put in your gauge and measurements and get custom sock knitting instructions.

Three 50 gram balls of standard sock yarn will make a pair of adult socks, four to be safe if you are very tall.

The generator works exactly to your measurements. If you want negative ease for better hold, you can subtract a bit from your circumference measurements. If you do, realize that stretching knitting sideways shortens it lengthwise, so be sure to add a bit to the height measurements to compensate!