How to do I calculate how much sand and cement needed for bedding mortar
An 80 pound bag is about half a cubic foot (sorry, as for metric, you're on your own).


  The finished volume of an 80# bag of Sacrete or Quikrete (pre-mixed cement, sand and gravel) is 0.6 cubic foot (stated on the bag). There are 27 cubic feet in a cubic yard. Dividing 27 cubic feet by the volume of the bag will give you the number of bags you need. –Google