The Knitter's Handy Guide to Yarn Requirements
This brochure-sized laminated card, can tell you how much yarn you'll need to complete almost any project. Sweaters, socks, mittens, gloves, hats, tams, and scarves are covered. Simple chart accounts for both gauge and size of project.
I carry this with me to the yarn store. If I see yarn I want to use for a sweater, I can be sure to get enough of it, before I even have a pattern in hand. Essential for shopping the sale bins!
It will also help you plan projects based on yarn in your stash. Do you have enough skeins for a child's sweater, or just a hat?
I use this card constantly.
