I would guess maybe 1/5 to 1/4 lb. per plant over the course of the plants life if you pick often to keep them productive but my experience is only with in ground bush beans. The diameter of the bucket would determine how many you can get in there but I would think at least 4 and maybe up to 6 would be OK in a standard 5 gallon bucket.

Thanks for the reply, I think the next time we grow them we're going with 4 per bucket. I don't want to move any right now because their roots are attached.

if you want beans, grow pole, not bush.. you could easily get a pound of beans per plant if they were pole. not to mention they take up less space so you could grow more of them.

Not entirely sure the what/why/expectations of what you are trying but... 4 4gallon buckets with 2 plants each? As for weight/ volume of beans... depends on what stage that you pick the beans. The plants will have beans growing at different stages.

You can crowd them more than that, 4-6 plants I agree. You want to be able to get enough beans at one time to cook up to eat fresh for a few good meals. You don't get the beans all at one time, you pick some every few days over the course of a few weeks. You will get an initial flush of beans, and should get a few more growths after that.