This is from IMAA site on what they consider giant scale >

What is Large or Giant Scale?

The concept of large or giant scale is generally considered to apply to radio controlled model aircraft with minimum wingspans of eighty (80) inches for monoplanes and sixty (60) inches for multi-wing aircraft. Ducted Fan aircraft with one hundred forty (140) inches combined length and width, measured from wing tip to wing tip at the widest point perpendicular to the fuselage and added to the length of the fuselage, excluding any protrusions. Quarter (1/4) scale replica's or larger with proper documentation (minimum 3 view drawing of an actual person carrying aircraft) which do not fit the size requirements will be permitted. However, the concept does not encompass radio controlled model aircraft so large as to have the potential of carrying a human being.


http://www.fly-imaa.org/imaa/about.html

HTH