In this paper we analyse the expected depth of random circuits
of fixed fanin f. Such circuits
are built a gate at a time, with the f inputs of each new gate being chosen randomly from
among the previously added gates. The depth of the new gate is defined to be one more
than the maximal depth of its input gates. We show that the expected depth of a random
circuit with n gates is bounded from above by ef ln n
and from below by 2.04 … f ln n.