Take the 7B people on Earth, and assume they're all families of 4. Put them each on 1/4 acre of land. Say that additional infrastructure like roads, schools, and retail will take an extra 50%.

That gives us roughly 1 million sq miles to hold the entire population of the planet on a comfortably-sized lot. That's 1/10 the size of the USA, about the size of the land area of Alaska plus Texas.

The people aren't going to be the problem with land usage.