NZ120 is built to a scale of 1:120, otherwise known as TT scale.

The New Zealand prototype runs on narrow-guage track 3 feet 6 inches (1067mm) gauge.  In TT scale this works out close enough to 9mm, or standard guage N-scale track.  We therefore use standard N guage track, wheels and mechanisms.

The nearest thing to standards or guidelines is set out in the original module standards.