For servers with 4 GB of RAM, set Maximum server memory to 2.048 MB. 2 GB is left for the OS.
For servers with 8 GB of RAM, set Maximum server memory to 5,120 MB. 3 GB is left for the OS.
For servers with 12 GB of RAM, set Maximum server memory to 8,192 MB. 4 GB is left for the OS.
For servers with more than 12 GB of RAM, leave 4 GB for the OS. The rest can be assigned to MS SQL Server.