Reckoning of time for Brahma.

1000 Mahayugas = 1 kalpa = 1 day (day only) of Brahma

(Two kalpas constitute a day and night of Brahma)

30 days of Brahma = 1 month of Brahma (259.2 billion human years)
12 months of Brahma = 1 year of Brahma (3.1104 trillion human years)
50 years of Brahma = 1 Pararddha
2 parardhas = 100 years of Brahma = 1 Para = 1 Mahakalpa (the lifespan of Brahma)(311.04 trillion human years)

One day of Brahma is divided into 10,000 parts called charanas. The charanas are divided as follows:
The Four Yugas 4 charanas (1,728,000 solar years) Satya Yuga
3 charanas (1,296,000 solar years) Treta Yuga
2 charanas (864,000 solar years) Dwapar Yuga
1 charanas (432,000 solar years) Kali Yuga
Source: [3]

The cycle repeats itself so altogether there are 1,000 cycles of mahayugas in one day of Brahma.

One cycle of the above four yugas is one mahayuga (4.32 million solar years)
as is confirmed by the Gita statement "sahasra-yuga paryantam ahar-yad brahmano viduh", meaning, a day of brahma is of 1000 mahayugas. Thus a day of Brahma, kalpa, is of duration: 4.32 billion solar years. Two kalpas constitute a day and night of Brahma
A manvantara consists of 71 mahayugas (306,720,000 solar years). Each Manvantara is ruled by a Manu.
After each manvantara follows one Sandhi Kala of the same duration as a Krita Yuga (1,728,000 = 4 Charana). (It is said that during a Sandhi Kala, the entire earth is submerged in water.)
A kalpa consists of a period of 1,728,000 solar years called Adi Sandhi, followed by 14 manvantaras and Sandhi Kalas.

A day of Brahma equals

(14 times 71 mahayugas) + (15 x 4 Charanas)

= 994 mahayugas + (60 Charanas)

= 994 mahayugas + (6 x 10) Charanas

= 994 mahayugas + 6 mahayugas

= 1,000 mahayugas