According to Official Guinness Records,
The largest LEGO® brick flag measures 3.47 m (11 ft 7 in) tall and 6.46 m (21 ft 2 in) wide, achieved by LEGOLAND® Discovery Centre Toronto (Canada) in Vaughan, Ontario, Canada, on 28 June 2018.248,062 bricks were used in the construction of the flag, which was built to celebrate the Canada Day holiday.
For a complete list of 2018 records, please visit 2018 Guinness Records in Canada.