There was actually a very easy to overlook statement made in the 2009 version of "The LEGO Book" which states that Minifigure Scale is 1:50 Scale. It says this about a stadium built for a Miniland in one of the LEGOLAND Parks, this stadium used normal Minifigures instead of the Brick Built Miniland Figures which is why they mentioned it. Other then that however there is no one exactly perfect universal "Minifigure Scale" to go by other than the fact that the build fits a Minifigure and has an environment that can accommodate them well based on the size of selves and furniture in a house or the controls and windows in the cockpit of a spaceship.