cell radius calculation
The first step: calculate the area of the entire cluster (S_cluster).
The second step: the area of a cell (S_cell) = S_cluster /7
Finally , S_cell = (3 * square(R) * squareroot(3))/2. Solve this equation to get R.
given the average traffic per user you can deduce the traffic of a region area having the total number of users.
knowing the capacity (traffic) that can be supported by a site you can compute the number of site needed. you will also need to have the area of the region to compute the area covered by a site. once you have this input you can deduce the radius with the formula
S_cell = (3 * square(R) * squareroot(3))/2
this way of computing the cell radius is theorical.
the typical method is what has been explained by pix below remembering that the
Maximum Allowed Path Loss=min(PathLoss DL, PathLoss UL) to avoid unbalanced link budget