Currently there are many practical tools or theoretical methods to plan and dimension GSM or UMTS radio networks but overlooks the algorithms for core networks because of its complexity. This paper introduces an algorithm for traffic and throughput dimensioning for Nb, Mc and Nc interfaces in UMTS core network. The analysis is based on the traffic and throughput generated or absorbed in the interfaces of network entities in UMTS network. This paper is targeted at helping wireless carriers plan and dimensioning their UMTS core networks.