An acre is 43560 square feet. Therefore one 1/2 mile row one foot wide would be 5.67% of an acre. Figure out how wide your rows need to be then start your calculations. Example ten acres would be 435,600 square feet 435600/2640/4= about 41 rows if your rows are 4' wide. Substitute the width of your row for the 4 in the above formula.