I got a 1 oz packet of spring barley seed (about 680 seeds), planted this spring, was 40+ sq. ft.. Total crop output was about 16 oz. Am going to plant these next spring, should have enough to actually brew then.
I don't know if this is representative of crop production or not, but the garden spot selected was not the best area of the yard, so, this may explain it.
The garden area for next year will be about 1,000 sq. ft. - I had tobacco in it this year. I will be planting that spring strain in about 1/4-1/3 the area, and got more seed of another spring strain (Robust) for the remainder area.
Also got a few (very few) seeds of Maris Otter winter strain - is in the ground now in a different area. Should be enough for a decent 2015/16 seed crop, then a full crop in the 2016/17 winter season.
For all the time and effort into growing barley, hardly seems worth it, except that with homegrown hops, I can say it's 100% homegrown beer, and 'I did it my way". Definitely not a money saving adventure. The tobacco is a different story, 1,000 sq ft of tobacco results in 25-35 lbs of tobacco, or a 3-4 year supply of cigarettes, at a cost of about 35 cents a pack (including the cost of buying the rolling papers).
Good luck with your barley grow, has been fun and interesting for me.