How to calculate how much yarn is needed

[millyandnans]

How can I tell how much yarn I need to make something, like say a purse?

I am BAD at math, so I don't know how to do it, like something with yardage and guage I'm sure.

It's tough when purchasing hand-spun yarn, and I want to start a bag project with custom yarn.

I'd generally like to order enough at once, too. So far I haven't made a really big project.

Thanks!

[Silver]

Find a pattern of a purse of similar size that you'd like to make and use the yardage as an estimate.