G gauge is a large size model railroad that because of its size can be made more durable, less likely to break making this the ideal gauge to be used outdoors. For this reason is has been dubbed "garden scale". The scale is 1:22.5 is a ratio 1 foot in model scale is 22.5 ft in real life. The inside width between rails is called gauge.  The gauge of G scale  is 1 3/4 inch. Because of this size a large area is needed to set up a layout. This layout is courtesy of Piper Hale.

Piper Hale