you can get it from 1 plant if you have good grow skills. otherwise if it is your first try... you will lose some to rippers, animals, bugs, and disease unless you have the means to deter... Figure you will harvest 1 plant for every 3 plants that you sow.. I would expect any outdoor plant that is given a veg time to produce at least 4 ounces... if you need a pound that means you would sow 12 plants to safely assume you will get a 1 pound harvest.
edit: chanced from 2 ounces per plant to 4 ounces per plant... it may not be obtainable for everybody but 4 ounces is a fair goal to shoot for one plant. Sowing 12 plants would grow 1-3 pounds of dried buds assuming you were pulling 4 ounces per plant.. more likely 1 pound after casualties to nature.