How much yarn?

Any suggestions on estimating the amount of yarn you need if you don’t have a specific pattern? I want to replicate a sweater, and I’m trying to get a general idea how much yarn I need. :thinking:
TIA!

How about something like this?

http://www.knittingfool.com/pages/yards1.cfm

What a great site!! Thanks so much!

“Knitter’s Handy Guide to Yarn Requirements,” by Ann Budd, is a neat triple-fold laminated card about the size of a #10 envelope that you can slip into your handbag or knitting bag when you go shopping for yarn. It lists yarn requirements by sweater type, size and gauge. It costs about $6 at yarn and book stores.