Antalon wrote:

Hello, is there a formula to calculating the Undead Type from AD&D or other OSR sources?

cheers

Step three on p252 under turn undead kinda gives you free reign on the Undead Type. Generally it relates to the Hit Die then +/- based on powers and significance of the creature.  The Vampire has 9 HD but a UT of 11 based on the other major powers this creature has.

The short answer is that there is no hard and fast rule but you can use current undead entries as a guide.