One day of Sri Brahmaa is called a kalp.
The duration of the four ages or yugas have been described as follows:
the duration of Kaliyuga is 432000 solar years, double is the duration of Dvapar yuga, triple is the duration of Treta yuga and quadruple is the duration of Stya-yuga. The four-yugas combied are called one divya-yuga or catur-yuga. The reign of one Manu is comprised of 71 such divya or catur-yugas. The span of life of fourteen Manus is the duration of one day of the life of Sri Brahma.
Similar also is the duration of one night of Sri Brahma.
At the end of one day of Sri Brahma or at the end of a kalp, partial annihilation takes place.
Source: Dasavatar, by His Divine Grace Srila Bhakti Ballabh Tirtha Goswami Maharaj