Does quarter bag refer to the amount of cement you would use per load? I often use a 1:2:3 mix for general purpose concrete. That would produce 6/4 of a foot or 1.5 cu ft. of concrete. (Slightly less, actually, because you have to divide the volume of the separate dry ingredients by 1.15 to get the true volume of the concrete that they will produce.) A 5 cu. ft. mixer would make a bigger load than that.