Once you get good at growing grass relavant to your growing conditions you can expect between 4-12ozs. per tray.Wheatgra SSKI ts.com has some poor grade wheat berries and 15ozs. is very unlikly.Thats one seed that I wont buy from them "wheat".I do get my barley,mungbean,alfalfa and buckwheat from them and like the quality and price point.There seed is a blend of differnt seeds with differant protein content whch makes for un-uniform germination and growth.Greenhouse growers dont use seed of this low-caliber do to lack of uniform growth looks bad to there costomers.Wheatgrassman.com has a good website and lots of info. on this subject matter.I have grown his hard red winter wheat and had good results here in central Illinois.I have never grown spring wheat but the fact most greenhouse growers use spring wheat speaks for itself.It appears as though the spring has a quicker turnover than winter and this would fit there buissness model very well.What kind of juicer will you be using to make your grass juice?Jeff.