Themix ratios for cement sand and stone for concrete can vary anywhere from 1 : 3.5 : 3.5 for low strength concrete
1 : 1.75 : 1.75 for high strength concrete.

These are to be mixed with "just enough" water for required workability and handleability but not more than that, in order not to decrease the concrete strength, as the water cement ratio W/C is one of the most important things for affecting concrete strength.