Singapore - Two of the world's most expensive residences in the world are currently inhabited by families who didn't even purchase the property.

How is this possible? It is - if you are US president Barack Obama or Britain's Queen Elizabeth II.

In a ranking compiled by entertainment website Mentalfloss.com, it listed the White House and Buckingham Palace as two of the world's most priciest homes in the world, along with other private residences owned by billionaires around the world.

Crowned the most expensive residence by Metalfloss.com, the official residence and office of the British monarchy Buckingham Palace became 'UK's most expensive family property' when it was estimated to be worth 935 million pounds (S$1.85 billion) by home valuation site Zoopla.co.uk in 2008, reported British news media The Telegraph.

Currently the palace is worth an around 1 billion pounds (S$1.97 billion), in its most recent estimation according to the UK's Nationwide Building Society in 2012. The report also added that Buckingham Palace has gone up in value by a whooping 9,000 per cent from its initial 11 million pounds (S$21.7 million) when Queen Elizabeth II ascended the throne in 1952.

However, the exact estimated value is disputed as Luisa Kroll from US business magazine Forbes reported in 2012 that the palace is worth around US$5 billion (S$6.2 billion). Either way, it is still the most expensive residence in the world.

Located in the city of Westminster, Buckingham Palace sits on 40 acres of land and has an astounding 775 rooms including 55 Royal and guest bedrooms and 78 bathrooms. It even has its own cinema and post office, said online reports.

Following closely behind the palace as the fourth most expensive residence in the world is 1600 Pennsylvania Avenue, also known as the White House.

Built in 1792, the White House boasts 132-rooms in total and is estimated to be worth $320 million (S$398 million), by real estate website Zillow.com.

Designed by Irish architect James Hoban, it became the official residence for the leader of the United States after second president John Adams and his family moved in after it was built in 1800, said Zillow.com.

Both residences are open to the public for guided tours and are used for official government matters such as meetings, announcements and gala dinners.

Though the White House and Buckingham Palace may be high in value, the other private homes in the rankings by Metalfloss.com are still impressive in their own ways.

Custom-built Antilla Mumbai, the residence of Indian billionaire Mukesh Ambani, took the first runner-up spot. According to Industry Leaders magazine, it called the 27-storey mansion as the world's most expensive home with an estimated value of 630 million pounds (S$1.2 billion) in 2010. The luxurious mansion with three helipads is sometimes considered the world's most expensive home by other news media.

Photos: AFP, Reuters, Bloomberg News, White House website, TheRichest, Youtube screengrabs, Wikipedia

Take a look at the world's 7 most expensive homes according to Mentalfloss.com