Here you go - straight from the net, not from my mouth, so I can't say how accurate it is - looks like S or HO would be closest, but none are right on:
Typical model railroad scales are (largest to smallest):
1:12 Large Scale
1:13.7 7/8 inch scale
1:20.3 G, Three-Foot Gauge on Gauge 1 Track
1:22.5 LGB and Bachman
1:24 Half scale
1:29 Aristo-Craft, USA Trains, standard gauge on #1 gauge
1:32 I scale
1:48 O scale
1:64 S scale
1:87.1 HO scale
1:120 TT scale
1:160 N scale
1:220 Z scale