That is impossible to answer, there are hundreds and hundreds of different types of African Cichlids. Some stay an inch long and others grow to be a foot, you have to be more specific.
What kind of Africans? If you get ones that stay under 5 inches I would say 5-6 max. If you got anyother fish that grow bigger then that I would suggest you get a bigger tank.
i have a 55 gal lake tanganiykan tank. i only have 9 cichlids and a synodontis. they are very teritorial. I definitely wouldn't consider any more for mine. it all depends on what size cichlids you want. usually 1 oz of mature fish per gallon.