Narrow gauge model railway scales and guages

There are dozens of combinations of model railway scales and gauges.  NGMRSC offers track from two manufacturers in three gauges, four product families, and five named scale-gauge combinations.

Scale / gauge name Scale ratio Model gauge Model mm per prototype foot Precisely represented prototype gauge Remark NGMRSC collection
OO9 1:76 9.0 4.0 684 mm / 2'3" Frequently used in United Kingdom. Often representing 2'0", 2'6", 1 metre, etc. gauges. PECO OO9 / HOn30 / HOe collection
HOn30 1:87 9.0 3.5 783 mm / 2'5" Frequently used in North America. Often representing 2'6" gauge. PECO OO9 / HOn30 / HOe collection
HOe 1:87 9.0 3.5 783 mm / 2'5" Frequently used in Europe, often representing 600 mm, 750 mm, 760 mm, or 800 mm gauges. PECO OO9 / HOn30 / HOe collection
HOn3 1:87 10.5 3.5 914 mm / 3'0" Frequently used in North America, representing three foot gauge. HOn3

and

Micro Engineering Company HOn3 collection
HOm 1:87 12.0 3.5 1044 mm / 3'5" Frequently used in Europe, often representing metre gauge. Peco HOm collection