In general, Automated Storage/Retrieval Systems (AS/RS) have racks of equal size. But higher utilization of warehouse storage can be achieved by using AS/RS with racks of different size. Therefore those systems are adequate and efficient in current environment. In this paper, travel time models are developed for AS/RS with racks of different size under randomized storage in each zone. Each zone has its own rack size. In order to confirm the proposed travel time models, some numerical examples are given.