We are constantly being asked what the various scales mean and how big are they. The following diagram courtesy of LGB should help. G GAUGE is 1:22.5 track width is 45mm 1 GAUGE is 1:32 track width is 45mm O GAUGE is 1:45 track width is 32mm OO GAUGE is 1:76 track width is 16.5mm HO GAUGE is 1:87 track width is 16.5mm TT GAUGE is 1:120 track width is 12mm N GAUGE is 1:160 track width is 9mm Z GAUGE is 1:220 track width is 6.5mm The track width is measured across the sleeper from rail head to rail head. HO/OO is the most popular with N coming second and G third. HO/OO uses exactly the same gauge track although the locos and rolling stock are slightly different scales.