• $N_{cpu}$ = Number of Available CPUs
• $U_{cpu}$ = Target utilization of those CPUs (0 ⇐ $U_{cpu}$ ⇐ 1)
• $W_c$ = Ratio of Wait time / Compute time

Following the formula: $ N_{threads} = N_{cpu} * U_{cpu} * (1 - W_c)$

You can determine the number of CPUs using Runtime:

int N_CPUS = Runtime.getRuntime().availableProcessors();