According to wikipedia ,it is approximately 1:11.3., All i know is working to 1inch and 1/16 from a full size drawing is a nightmare,Things like buffer centers and heights do not add up, So like all the other Gauges listed above it is all a compromise,all good fun thou, Do not mention gauge to my wife, as that is my nickname as i have a liking for them, 16mm,g1, 0,00, My next loco is 3 1/2, and ive modeled 7 1/4, The best gauge i have modeled in was 7 1/4 inch gauge ,it was 1 1/2 to the foot and this made working from prototype stuff much more accurate.