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.
4 oz per plant is a more than fair goal. If I dont pull at least a qp per, i consider it a failure on my part....
The problem for me, and I'm sure others, with having more plants, is the $ is takes to be successful with those plants. 2 years ago, I planted 20 to ensure I would have enough to last me the year, figuring I'd get a minimum of 4 oz per plant... and have more than enough for the year, and also figuring I may loose one or something like that.
Well, unforseen and unavoidable circumstances occured, and I couldnt afford all the nutes required to obtain that 4 oz per... I ended up with 1 that got 12 oz, and the rest were between 1/2 and 1.
Last year, still dealing with the financial issues, I decided to plant 3, and give them everything I could afford, and ended up with enough to last me till just a few weeks ago.
So the moral of the story is... More plants does NOT always equal more weed....