What is a units sight range in tiles?

What is an xcom soldiers sight range in straight line tiles as well as diagonal tiles? also is there an in game graphic or other graphical picture that depicts this? Are there Units that can see further or shorter than an xcom soldiers?

The sight range in cells is 17. Diagonally it is also approximately 12 =~ 17 / sqrt(2), but was not tested too well.

All characters have the same sight range, which is 27 in some obscure internal units.

In this question we've tried to match those config units to cells, with a limited success. It is either
cells = (units / 1.5) - 1 or
cells = units * 0.625 with funny rounding.