Assuming you wish to used bagged 'pre-mixed' concrete, the industry standard is 1/2 cubic foot yield from a 60 pound bag. Keep in mind that the true weight will vary due to such things as sand/portland/aggregate ratios.
But for a simple answer, you will be close with 3240 pounds.
60 pounds per 1/2 cubic foot, = 120 pounds for each cubic foot.
27 cubic ft. per yard
120 X 27 = 3240