A mansion is a large dwelling place from the French word maison which means house. It is a large residence, or a house of someone of considerable importance or grandeur.
But in the 19th century the meaning of mansion expanded and this time it came to be used in the sense of 'the designation of the large buildings, divided into 'flats', which began to be erected in London about 1860,' used in the plural, as 'Belgrave Mansions' or 'Albert Mansions,' and sometimes even referred to as 'a mansions.' Considering this, it seems clear that the Japanese mansion in particular is a direct adaptation of the English manner of naming elegant apartment buildings.
Anecdotal sources suggest that the general consensus in the United States is a house that has 7,000 sqft or more is considered a Mansion.
Mini mansions are also elegant houses that offers luxury living like those offered in mansions but they are smaller versions; those that are ranging a living area of 5,000 sqft and below.
Tortoise Island Canal Front Mini Mansion - LuxuryRealEstate.com™
There is no one design, style or size that embodies a luxury home. It could be a sprawling 15,000-square-foot French manor set on several rolling acres, or it could be a 4,000-square-foot contemporary home nestled into the side of a mountain.
Although it's difficult to quantify exactly what luxury means, most buyers think they know it when they see it. Check out some tips for buying luxury real estate at Investopedia.com.