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Really?

You've got small branch nuggets that can go from .0125 grams all the way up to top colas that can come in at 5 pounds (maybe bigger) So the average between the two is 2.5 pounds. (heh, right...) So the average bud weights 2.5 pounds. (If your reading this, please note its written with sincere sarcasm).

To cover what's already been said, there is no average bud weight, because plants are different, conditions are different, every possible variable all the way down to humidity will effect the size of your buds, so nobody can tell you an average, there is no such thing. You can produce a single cola plant with a 2.5 pound cola, or a bush of the same strain that yeilds 6 pounds total... in both cases the bud size and weight will be different even if it tastes the exact same.