I am making dinner for a large group of people tonight an would like to do green beans as a side. Normally I use canned but I'd like to do fr

I would highly suggest doing fresh. Canned green beans, unlike canned starchy beans, are not compatible with the real deal and they don't taste very good in my humble opinion.

3 lbs should be enough for 12 people, if it's one of 2+ sides. 4-5lbs if it's the only side dish.

I never measure or weigh my veggies, I just give it my best guess. Just throw a good handful into the produce bag (per guest). And then throw in one extra for good luck. I always consider that handful to be a portion and it always serves me well. I always have enough to go around.

Frozen green beans will be much better than canned.

Fresh got cut off! I'd like to do fresh beans instead of canned. However, I doubt anyone but me at this dinner will care if they are fresh or canned.