No, the Pentagon is not the biggest building in the world. The title of largest building in the world is currently held by The Venetian Macao, a hotel and casino resort in Macau, China. The Venetian Macao has a total floor area of over 10 million square feet (929,000 square meters), while the Pentagon only has a total floor area of about 6.5 million square feet (600,000 square meters).