If you have access to examples of any ape or hominid skulls, (Homo sapiens, Neanderthal, Australopithecus, Chimpanzee, etc), you can use this video to show students how to make a reasonably accurate comparison of brain size in different species. All that is needed is a length of string and ruler or meter stick.The video explains the procedure. The included papers are applicable to the skulls I use in class, but you can modify for your needs if you have others available. This is easily accessible