1.80lb bag of cement?

Question:how many cubic feet can i get out of 1 80lb bag of cement using sand and gravel?

Answers:
The actual cement required for concrete is affected by the choice of the maximum coarse aggregate size. As the maximum coarse aggregate size is decreased the cement content must increase to provide the required quantity of cement paste to coat all of the aggregate particles.

Assume that the proportions will be made based on one part being a cubic foot (this is convenient since a 94 lb. bag of cement is 1 cubic foot of bulk material). For a 3/4" maximum coarse aggregate, the mixture would be 1 part portland cement, 2 1/2 parts sand, 2 1/2 parts coarse aggregate, and 1/2 part water. The sum of the parts is 6 ½. In general the final volume of concrete produced will be approximately 2/3 of the sum of all the volumes included in the mixture. Therefore the approximate volume of this concrete mixture is 4.3 cubic feet.

If you adjust the above mixture based on a 80 lb. bag of cement, then you will produce 3.7 cu. ft. per bag approximately.