One Year of celestial gods, consisting of 30*12 days is equal to 360 years on the plane of earth.12000 years of celestial gods( 12000*360) corresponds to one Maha Yuga(Cycle of 4 Yugas) on earth plane which corresponds to 4 million and 320 thousand years. 1000 such maha yugas comprises one day of Brahma.This is called Kalp.Same Duration is Brahma’s night. By these calculations Brahma lives for 100 years. By calculations of earth plane, it is 311 trillion 40 billion years which is the Age of the Universe.
Vedic Calculations of time of Yugas are:
Kali Yuga: 432,000 years.
Dwapar Yuga: 864,000 years.
Treta Yuga: 1296,000 years.
Satya Yuga: 1728, 000 years.
Together they comprise one Maha Yuga(Cycle) which is of duration 4320000 years.
One Thousand Maha Yugas comprise one day of Brahma, which is Kalp and whose duration is 4320000000 years, of equal duration is the night. Entire duration of Universe is equal to Brahma’s life span of 100 years which equals 311 trillion 40 billion years. Brahma is also a soul who discharges duties for God in creation of Universe.Hence, Brahma is also within cycle of life and death. Rarely, when no soul is eligible to perform the duties of Brahma at time of creation of the world, God Himself becomes Brahma.
At the advent (beginning) of Brahma’s day , all living entities emanate(manifest) from the unmanifest source(state). And at the fall of his night, all embodied beings again merge into their unmanifest source.
At the end of Brahma’s day, corresponding to one kalp of 4320000000 years, all planterary systems up to Mahar Loka are destroyed. This is called partial dissolution.
At the end of Brahma’s life of 100 years, which corresponds to 311 trillion 40 billion years , entire Universe is dissolved.At this time , entire material creation is finished.
100 years of Brahma’s life are equal to one breath of Maha Vishnu. Each Universe has one Brahma, one Vishnu and one Shiva. So there are innumerable Brahmas, Vishnus and Shivas in innumerable Universes. All Vishnus in all the Universes are expansions of Maha Vishnu.