if NFA has $n$ states , then states in DFA will be determined by set of subsets of the states of the NFA.
$1\leq $ Number of states in equivalent DFA $\leq 2^n$, where $n$ is number of states in NFA.
say NFA has two states , $q_0$ and $q_1$ , then DFA may have ,any to all, of $\{\{\},\{q_0\},\{q_1\},\{q_0,q_1\}\}$