How much yarn?

I've posted this previously on another space but it's worth re-posting here as I am afraid it may be lost in the shuffle of new email addresses and web pages.

To make a sweater,

How much yarn to buy? 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. Approximate Gauge 4" 32+ s x 24 - 32s x 20-24s x 16 - 20s x 26 r 12-16s x 8-12s x Needle Size 00-2 2-4 4-6 7-9 10-10 1/2 14-15 Cotton approx yds/lb 4200 2100 1260 840 Cotton 10/2 5/2 3/2 2/2 or 1/1 Wool approx yds/lb 6720 2800 1200-1800 1020 560 300 worsted(wool,acrylic) 1/13 or 2/24 2/13 , 3/15 , 1/5.5 2/7.5, 3/11 , 1/3.5 3/6.4 , 4/8, 1/2 3/4 , 1/1 1/.5 Shetland Cobweb Lace Weight Jumper Weight 3 Ply yarn 4 Ply yarn Chunky Handknitting Baby Fingering Sport Worsted Bulky, Aran Very Bulky, Icelandic Infant 600 500 400 300 Toddler 800 700 600 500 400 350 6-8 1250 1100 950 800 700 550 10-12 1300 1200 1100 950 800 700 Teen 1400 1300 1200 1000 900 800 S 1600 1400 1300 1050 950 900 M 1800 1600 1400 1200 1000 950 L 2000 1800 1600 1400 1200 1000 XL 2000 1800 1600 1400 1200 XXL or man's 2000 1800 1600 1400