It's about as big as Grand Central Station
(formally Grand Central Terminal, a.k.a. Grand Central, a.k.a. GCT) (New York City, New York) (total terminal area).
Grand Central station, the largest train station in the world by platform count, measures 20 hectares in total area. The large flag which was suspended from the concourse ceiling following the September 11th 2001 terrorist attacks measures about 0.007 hectares.
It's about nine-tenths as big as Washington National Cathedral
In other words, 20 hectares is 0.87 times the size of Washington National Cathedral, and the size of Washington National Cathedral is 1.1 times that amount.(a.k.a. Cathedral Church of Saint Peter and Saint Paul) (Washington, DC) (total plot)
Sitting atop the 115 m (377 ft) tall Mount Saint Alban at the corner of Massachusetts and Wisconsin Avenues, Washington National Cathedral sits on a landscaped, 23 hectares plot.
It's about nine-tenths as big as The United States Capitol
In other words, 20 hectares is 0.87 times the size of The United States Capitol, and the size of The United States Capitol is 1.1 times that amount.(Washington, DC) (Immediate grounds size)
The grounds of United States Capitol, at the center of Washington DC's quadrants, consists of about seventeen buildings on a 23 hectares plot. While the Capitol Building is the central feature, other buildings include the Supreme Court Buildings and the Library of Congress Buildings, as well as several monuments and sculptures.
It's about four-fifths as big as Soccer City
In other words, 20 hectares is 0.83 times the size of Soccer City , and the size of Soccer City is 1.2 times that amount.(a.k.a. FNB Stadium, a.k.a. First National Bank Stadium, a.k.a. The Calabash) (Cape Town, Western Cape province, South Africa) (Nasrec, Johannesburg, Gauteng, South Africa) (total stadium footprint)
Soccer City, the football (soccer) and rugby stadium measures 24 hectares and is the largest stadium in the country of South Africa and largest on the continent of Africa. The Stadium was the site of Nelson Mandela's first public speech upon being released from prison, and the site of Mandela's public memorial in 2013.
It's about one-and-three-tenths times as big as The Citadelle
In other words, 20 hectares is 1.3 times the size of The Citadelle, and the size of The Citadelle is 0.77 times that amount.(a.k.a. La Citadelle, a.k.a. Québec Citadelle, a.k.a. The Citadel) (Québec City, Quebec, Canada) (for the fortified enclosure)
The Citadelle of Quebec, containing Canada's oldest military buildings measures about 1.50 hectares in total area. The fortress sits on a 90-meter cliffside, overlooking the St. Lawrence River.
It's about one-and-one-third times as big as Eden Park
In other words, 20 hectares is 1.33 times the size of Eden Park, and the size of Eden Park is 0.752 times that amount.(Auckland, Auckland Province, New Zealand) (total grounds)
The largest stadium in New Zealand, Eden Park in Auckland measures about 15 hectares over its total grounds. It is primarily a rugby and cricket stadium. The Park offers rooftop tours, where fans can walk along the 39-meters-high roof of the stands.
It's about one-and-two-fifths times as big as The Pentagon
In other words, 20 hectares is 1.45 times the size of The Pentagon, and the size of The Pentagon is 0.69 times that amount.(a.k.a. United States Department of Defense Headquarters) (Washington, D.C.) (total floor area)
The Pentagon, the world's largest office building, contains a total floor area of 13.80 hectares. Built during World War II, the designers compensated for the steel rations then in effect by using 310,000 cu. m of concrete in the construction efforts.