Each seed will hopefully produce a cornstalk, bearing 1-3 ears of corn.
Perhaps you can measure how many corn kernels you have in one ounce, then extrapolate to 12 ounces, therefore predicting the yield of corn from 12 ounces of corn kernels.
Other factors will also come into play....environmental, pests, soil conditions.....
As previous poster said, it's based on how many plants you get and how much space you give each plant. 12oz should give you enough plants to produce a lot of corn in the garden situation if you space them 8" apart in 30" rows.
Some of the sweet corn varieties may have 3X more seed than another variety in 12 oz. It's all about seed count/lb.