This paper concerns a new model for estimating the wire length distribution (WLD) of a system-on-a-chip (SoC). The WLD represents the correlation between wire length and the number of interconnects, and we can predict circuit performances such as power consumption, maximum clock frequency, and chip size from the WLD. A WLD model considering core utilization has been proposed, and the core utilization has a large impact on circuit performance. However, the WLD model can treat only a one-function circuit. We propose a new WLD model considering core utilization to estimate the wire length distribution of SoC, which consists of several different-function macroblocks. We present an optimization method to determine each core utilization of macroblocks.