This paper addresses the retrieval batch size which the bi -directional multi -rack carousel system can be feasible. Each rack of the carousel system turns clockwise or counterclockwise rotation. The items that customers order are retrieved from the bins of the carousel with batch size. The mathematical model is formulated to represent the rotary travel distance and the retrieval lead time for retrieval batch size in an bi -directional carousel system. The rotary travel distance is the distance which the carousel system rotates for retrieval of all items included in a batch. The retrieval lead time is the time interval from retrieval starting time to retrieval finishing time for retrieval of all items included in a batch. The retrieval batch size that the carousel system can be feasible is obtained. A numerical example is shown to explain the solution procedure. The rotary travel distance and retrieval lead time are obtained through simulation approach in a numerical example.