This question gets asked hundreds of times everyday and every time it gets the same 20 answers "Its impossible to tell". There is so many things that are different from grower to grower like styles(soil?hydro?) how long they have been growing, how well they know the strain, temps, bulbs and distances and it goes on and on and on.
Assuming you get 0.5grams per watt or better than your looking at 3600(watts)*0.5=1800grams/28(grams to ounce)=64ounces/16(ounces to pound)=4lbs if everything goes right. Even then thats just a rough idea you could end up with a pound or get 2gram/watt.
