The shared memory area calculation for an IMS-enabled enterprise server is essentially the same as for a Web services enterprise server. Your calculation should also include 512 bytes for each 3270 client that will be concurrently connected to the enterprise server. Note that you must include your message processing regions in the total number of service execution processes.
If you are using CICS or JCL applications in the same enterprise server you will also need to perform the calculations described in Shared Memory Area in the chapter Configuring MSS-enabled Enterprise Servers for CICS and Shared Memory Area in the chapter Configuring MSSenabled Enterprise Servers for JCL and add the relevant results to the figure you calculcated for IMS.