I'm terrible at that - but I know people who can do that almost to the exact weight. Of course, they have years upon years of breaking up pounds of the stuff at a time.

The problem with eyeballing is that some weed is very dense & heavy, while others is a little fluffy.

We always do ounces, and although the weight is alway good, the actual volume can vary by quite a bit.

I'm sure someone else will come along with a rule of thumb or something - or you can do a little search on the site. I would think it's been discussed before.