Two ways
It depends on whether you want to adjust your bet based on penetration, or just use the raw running count.
If you just use the raw running count, you bet minimum until the "key" (-2 in 6D, if I recall correctly), and typically increase one unit per point after that. A RC of +4 in KO is supposed to be the same as a Hi-Lo TC of +4.
If you want to adjust for penetration, there have been various posts about the numbers. I don't have them memorized since I mostly play 2D.