depends on a lot, what kind of nutes are you using, how large are you going to let them get before you put them into flowering.
its hard to say from your picture but i'd guess they were around 12 inches high, i'd let them veg another 2 or 3 weeks, get around 18 inches anyway. 11 good healthy 18 inch plants under a 1k hps in 2.5 gallon pots could conceivably yield a couple pounds, but a more realistic yield would be 3/4 of a pound to 1 pound once its all dried and cured