This paper proposes a scalable algorithm for quality of service (QoS) based routing. This type of routing is one of the main components for supporting new multimedia applications on the Internet. The algorithm takes into account the available bandwidth, the transmission delay and the packet loss probability for each link in route computation. This three-metric algorithm is as complex as a two-metric algorithm and provides a better characterization of application requirements. The mechanism was implemented using a network simulator and the results obtained are 25% better than the classical approach.