https://ddowiki.com/page/Turn_Undead
Turning check:
Your effective turning level.
A die roll (1d20 + your charisma modifier) that adds a positive/negative bonus (from -4 to +4) according to the table on the right.
Any bonus to your maximum hit dice from other sources.
Turning check result
Highest hit dice turned
up to 0 Turning value - 4
1-3 Turning value - 3
4-6 Turning value - 2
7-9 Turning value - 1
10-12 Turning value
13-15 Turning value + 1
16-18 Turning value + 2
19-21 Turning value + 3
22+ Turning value + 4