Poruthams are chalked out after the study of the birth stars of both the boy and the girl who are contemplating marriage. The sages had initially devised 20 poruthams but now only 10 are in use. According to them, there are 27 birth stars (nakshatras) for each person in an oval configuration which constitutes a zodiac. The zodiac influences the person through the nine planets (navgrahas).
The 10 poruthams (kootas) thus chalked out are: dinam, ganam, yoni, rasi, rasiyathipaty, rajju, vedha, vasya, mahendram and stree deergham.