While I’m just using data from the web and not actually measuring the spots in the parking lot atm, the basic size of a parking spot is 8x16 feet (128 sq feet). That works out to just over 11m^2 if Google can be trusted with the conversion.
Larger spots can go up to 10x20 feet which would work out to just over 18m^2.
And a 4mx4m room is not a small flat, that’s a small room in a small flat. But we may have cultural differences in what we determine small here.