How much yarn do you buy to knit a sweater?  I guess the answer is really pretty simple:  or maybe not.  If you're in the store, and you see a yarn you absolutely have to have, buy at least a dozen skeins.  That's the simple answer.   The complicated one is buy pretty close to what you need.  I've compiled the information below from a lot of different sources and they didn't all agree.  I've tried to even out the numbers so they make sense.   So if your knitting pattern calls for a particular yarn or a particular number of skeins, please use it as the primary source for determining how much yarn to buy.  It always pays to buy 10 percent more than you think you will need.  You can always knit a hat or mittens or socks with the leftovers.  But, if you run out on the left sleeve, you're in trouble!

Number of yards given is for a long-sleeved sweater.  You can subtract 10 percent for short sleeves or 20% for sleeveless.   Please note for special yarns like chenille or mohair, the length will be much greater per lb because of their great loftiness. 

The cardinal rule is - ALWAYS make a swatch! The numbers given are a rule of thumb.   Variations can occur due to humidity, tension, type of yarn, and a hundred other factors.