50.8 cm x 50.8 cm

Photo from Wikimedia Commons
Monopoly Board
The board game that has ended more friendships than social media/Toys & Games
A standard Monopoly board is 50.8 centimeters (20 inches) square when unfolded, giving it an area of about 0.258 square meters. The complete game set, including board, pieces, cards, money, houses, and hotels, weighs approximately 900 grams. Monopoly was first published by Parker Brothers in 1935 and has since been sold in over 114 countries and 47 languages. The longest game on record lasted 70 days. The game was originally designed to demonstrate the problems of wealth concentration, which it does very effectively by making everyone at the table miserable except one person.
Measurements
Board, pieces, cards, and money