In November 2007 Filipina Grace Galindez-Gupana made a big flag covering an area of 13 football fields, that is, 660 meters (2,165 feet) long and 100meters (330 feet) wide. The 18,847 m2 flag weighted 5.2 metric tons.
And that of course was a Guinness World Records.
However, the largest flag that is regularly hoisted is the Brazilian national flag flown in the Square of the Three Powers in Brasilia, Brazilian capital. This flag weights about 600 kilograms (1,300 pounds) and has 7,000 square meters (70×100 m = 230×330 feet).