This article explores the use of a new relation correcting theoretical (DPn) with experimental values obtained in the dead-end polymerization of styrene with azocompound. The syntheses were realized for several starting initiator-to-monomer ratios (C-0's); values comprised between 10 and 0.1%, and the experimental (DPn) were obtained by size exclusion chromatography. Concerning the theoretical (DPn), a new relation is proposed considering the loss of initiating radicals [I .] used in primary termination and both stationary states of I . and M . (macromolecular radicals) introduced as Bamford. Finally, ((DPn) over bar)(cum), previously defined by us, is introduced to consider the monomer conversion during oligomerization. Our relation fit very well in a large range of C-0's, contrary to the application of the usual Mayo rule, and a discussion of validity is proposed. Our model also allows the prediction of ((DPn) over bar)(cum) in a large range of telechelic oligomers from 10 to 150.