The road outside my house now is pretty typical for everywhere I've lived (five states and counting). It's two lanes wide, so let's say 25 feet across (pretty sure it's not actually that wide but we'll go with it). One lane goes to neighbor across the street, one to me, so 12.5 feet by the width of my yard. It's been a while since I've measured my full yard, but it's somewhere around 60 feet I'd reckon. We'll go with a house that's wider rather than deeper for maximizing road space and round up to 100. That's 1250 feet squared for the road, or roughly 0.03 acres.

If you added up every tiny little bit of everything you could maybe add 0.1 acres with the neighborhoods that have entry signs or something, but I really don't see how you'd get up to an acre. And certainly most people aren't talking about lot sizing doing all this extra math. There's certainly inefficiencies in urban sprawl that come into play though.