"Two kalpas constitute a day and night of Brahma. A "month of Brahma" is supposed to contain thirty such days (including nights), or 259.2 billion years. According to the Mahabharata, 12 months of Brahma (=360 days) constitute his year, and 100 such years the life cycle of the universe. Fifty years of Brahma are supposed to have elapsed, and we are now in the shvetavaraha-kalpa of the fifty-first; at the end of a Kalpa the world is destroyed "
According to Bhagvad Gita it is understood that material universe is limited.There is a mention of four types of Yugas (ages) Satya ,Treta,Dvapara and Kali..Satya Yuga lasts for 1,728,000 years,Treta 1,296,000,Dvapara 8,64,000 and Kalki,the Yuga we are living in for over past 5000 years lasts for 4,32,000 years . In Kali-yuga vice increases to such a point that at the termination of the yuga the Supreme Lord Himself appears as the Kalki avatāra, vanquishes the demons, saves his devotees, and commences another Satya-yuga. Then the process is set rolling again.These four Yugas ,rotating a thousand times ,comprise one day(this one day is known as Kalpa which consists of a thousand cycles of Yugas ) of Brahma and it takes the same number to comprise one night. Brahma lives one hundred of such years and then dies.(Bhagavad -Gita) .
