understanding HO Scale 1:87
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Understanding the Term HO Scale as it relates to the diecast model car industry

Some History on the term:

HO scale as it relates to the 1:87 diecast model car industry

HO scale (H0 scale in continental Europe) is the most popular scale of model railway in most of the world (outside the United Kingdom, where the slightly larger in scale OO scale is most common). The name is derived from the German Halb-null ("half-zero"), because its 1:87 scale is approximately half that of O scale.

In HO scale, 3.5 millimetres represents 1 real foot; this awkward ratio works out to about 1:87.086. In HO, rails are usually spaced 16.5 millimeters apart which models the standard railroad gauge of 4' 8.5" or 1435mm.


A grain silo on the Chesapeake Bay & Western RR layout.
The visitors center in Suffolk, VA has this layout to show the railroads in the county.
A Newport News Public Schools bus is seen here on the Chesapeake Bay & Western RR layout.HO scale trains first appeared in the United Kingdom in the 1930s, originally as an alternative to OO scale. It proved unsuitable for scale modelling UK trains. However, it became very popular in the United States, where it took off in the late 1950s after interest in model railroads as toys began to decline and more emphasis began to be placed on realism in response to hobbyist demand. While HO scale is by nature more delicate than O scale, its smaller size allows modelers to fit more details and more scale miles into a comparable area.

In the 1960s, as HO scale began to overtake O scale in popularity, even the stalwarts of other sizes, including Gilbert (makers of American Flyer) and Lionel Corporation began manufacturing HO trains.

Currently, HO is the most popular model railroad scale in both continental Europe and North America, whereas OO gauge is still dominant in Britain. Today, HO locomotives, rolling stock (cars or carriages), buildings, and scenery are available from a large number of manufacturers in a variety of price brackets.

The Gauge
HO scale has several narrower gauges to represent narrow gauge trains in the same scale as their HO counterparts.

Name Gauge Prototype Notes
HO 16,5 mm Standard gauge
HOm 12 mm Meter gauge
HOn3-1/2 12 mm 3'6" gauge 3'6" is the "standard" gauge in much of Africa, Queensland (Aus), New Zealand and also non-Shinkansen lines in Japan
HOn3 10.5 mm 36" gauge
HOn30 / HOe 9 mm 30" gauge Typically for lines in 24-30" gauge. Known as HOe in Europe
HOz / HOf 6,5 mm 15" gauge Known as HOf in Europe

In addition, the term HO, when used in the hobby of slot car racing, does not denote a precise scale, but a general size of track on which the cars can range from 1:87 to approximately 1:64 scale.

Modern HO trains run on realistic-looking two-rail track, which is powered by direct current (varying the voltage applied to the rails to change the speed, and polarity to change direction), or by Digital Command Control (sending commands to a decoder in each locomotive). Some trains, most notably by Märklin of Germany, run on alternating current, supplied by a "third rail" consisting of small bumps on each tie down the center of the track.

Curved Track
Commonly manufactured curved track in HO scale may have a radius of around 360mm which models a full-scale curved radius of 32 metres. This is an extremely tight curve which may be more representative of a 19th Century mountain pass, or a Light Rail in-road system. Compare this with modern Very Fast Trains which use a minimum curvature radius of 4000 metres!

Note that the inner curved rail will have a radius 16.5mm shorter than the outer curved rail! Additionally, if you would like to have 2 tracks curving alongside each other then you will need the outer track to have a higher radius than the inner track. One manufacturer makes a No.1 Curved radius of 371mm, a No.2 Curved radius of 438mm and a No.3 curved radius of 505mm for this purpose.

There also exists a finer, more prototype-accurate set of HO model railroad standards called Proto:87, designed to forego the usual compromises used in the manufacture of model railroad components. Its track gauge and scale are the same, but components like wheels and track have been narrowed down to correct 1:87 scale.

Additonal Resources

Understanding Scale
1:18 Scale
1:24 Scale
Diecast Directory
See ALL 1:87 scale diecast model cars (in stock and out of stock)
See only IN STOCK 1:87 scale diecast model cars


This page was last modified 26 January 2007.
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