Pick a ip class, this will determine the number of device that the subnet can be assigned to
Choose class A for 16,777,214 hosts choose class B for 65,534 hosts or Class C for 254 also class A usually ranges from 10.0.0.1-10.255.255.254,class B 172.16.0.1-172.31.255.254 and class C 192.168.x.0-192.168.x.254 replace x with any number between 0 and 255