mg of particular drug per cc is drug concentration, there is no correlation from one brand to another or one drug to another; so one drug might be 250mg/cc, another only 50mg/cc; its all about how the manufacturor saw fit to load the oil
cc meassures volume and mg meassures wheight, so you can´t compare them like that. If a steroid has the strength of 250mg per cc it means it has 250mg of the active substance in one cc oil or water. 1cc is also the same as 1ml