It's about one-third as big as Alcatraz.
In other words, the size of Alcatraz is 2.90 times 31.50 dunams.(a.k.a. The Rock) (California)
Alcatraz Island measures 89 dunams. It is known a part of the Golden Gate National Recreation Area, and has historically served as a lighthouse, fort, military prison, and — most famously — a federal prison.
It's about three times as big as a City Block (Manhattan).
In other words, the size of a City Block (Manhattan) is 0.30 times 31.50 dunams.(per Bridges, William - 1811 Commissioner's Plan for New York City) (approximate)
A Manhattan city block measures about 200 m between the Northeast-Southwest streets by about 60 m between the Northwest-Southeast streets for a total area of about 10 dunams. There are roughly 2,000 blocks within the city, representing one of the most prolific applications of the city planning grid plan in history.
It's about three-tenths as big as Ellis Island.
In other words, 31.50 dunams is 0.2840 times the size of Ellis Island, and the size of Ellis Island is 3.520 times that amount.(Jersey City, New Jersey and New York City, New York)(now officially part of the Statue of Liberty National Monument)
Ellis Island, home of the Ellis Island Immigration Station, is 111 dunams in total area. Nine-tenths of the island were artificially created after the New York-New Jersey borders had already been defined, leading to a sovereignty dispute which was settled by the US Supreme Court in 1998.
It's about one-fourth as big as The Pentagon.
In other words, 31.50 dunams is 0.2280 times the size of The Pentagon, and the size of The Pentagon is 4.390 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 138 dunams. 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.
It's about one-fifth as big as Grand Central Station.
In other words, the size of Grand Central Station is 5 times 31.50 dunams.(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 200 dunams in total area. The large flag which was suspended from the concourse ceiling following the September 11th 2001 terrorist attacks measures about 0.07 dunams.
It's about five times as big as The White House.
In other words, 31.50 dunams is 5.10 times the size of The White House, and the size of The White House is 0.20 times that amount.(Washington, DC) (including wings)
Housing the presidency, the White House occupies six stories and a total of 6.20 dunams of floor space. This space includes 132 rooms, 35 bathrooms, 28 fireplaces, and 3 elevators, as well as a tennis court, bowling alley, movie theater, jogging track, swimming pool, and putting green.
It's about six times as big as a Football field.
In other words, 31.50 dunams is 5.8865135090 times the size of a Football field, and the size of a Football field is 0.16987984460 times that amount.(American) (per NFL regulation)
Per NFL rules, a football field should measure 109.728 m (120 yards) long by 48.768 m wide, for a total area of 5.3512151040 dunams. Due to a blizzard, the first NFL playoff game in 1932 was held indoors in Chicago Stadium (it was also the first indoor game) on a field measuring just 55 m by 40.0 m, for a total area of 2.20 dunams.