One ball wonders

I have this 'thing' - I always wonder how much  I can make out of something!
For example, take one ball of 50 gram wool, how much does that knit up?
Answer: ..... this much!

It's the start of the vest that I'm knitting for my hubby, I'm actually pleasantly surprised how much it knit up!  (is knit up the right words??)

Do you wonder such crazy things?

Can you tell me this? 
When it comes to fabric, how much does a jelly roll make or charm squares?