Hahahahaha, what is even that! European cities are so different from the USA cities, also it's really meaningful how you used "americans" to indicate only US citizens ;-D

Moreover, averages are not really statistically meaningful if you model data that isn't normally distributed (aka, somehow gaussian).

Last time I checked I saw that things like house size (btw, is it really a measure of wealth? Like the zeros in a fiat bank account, I suppose) are not normally distributed...in fact are more right skewed. Thus, you're better off using median.

PS. Since you're referring to americans, what's the average house size in Mexico, Canada, El Salvador, Nicaragua, Brazil, Argentina, Cile, ....