PURPORT

In one day of Brahma, there are 14 Manus, and all of them are considered to be manvantara-avataras of the Supreme Personality of Godhead. Thus in one month of Brahma's life, there are 420 manvantara-avataras, or Manus. In one year (360 days) of Brahma's life, there are 5,040 Manu incarnations. Thus for the one hundred years of Brahma's life, there is a total of 504,000 manvantara-avataras.