Sizing Guide Sizing is based on length + width depending on how full you’d like your arch to be! 7ft balloon arch paired with one of our mini arched walls. 8ft balloon arch 9ft balloon arch paired with one of our main backdrops. 10ft balloon arch paired with our two mini arched walls. 11ft balloon arch 13ft balloon arch paired with our main arched backdrops and one of our mini walls. 17 ft balloon arch paired with one of our main arched walls. 18 ft balloon arch paired with all three of our trio arched walls.