According to the Virginia Tech people, it is about 3 total acres per cow/calf unit in Virginia (about half an acre for hay production in addition to 2.5 acres for grazing). Let' say you can get about 620 lbs of meat per cow. And let's say Everybody on Earth ate 0.5 lb of meat a day. This is being super generous, as the average American already eats more than that and if we were leaning into free range beef that number would certainly more than double.