HO scale is the single most popular model train scale in the world.  The wide range of models produced in HO scale makes this a perfect scale for model train layouts, miniature wargaming, and precise model building.  This purpose of the scale was to make smaller, cheaper models that were still large enough to provide for great detail.

Airfix First Series HO/OO scale USMC and Roco Minitanks HO scale Tank Destroyer M36 Z-206.

Over 100 years ago there were four popular scales for model trains, they were numbered as 0, 1, 2 and 3 scales.  The smallest of these scales was 0 at 1/48th scale.  People wanted an even smaller size train so they could set up train sets that took up less room and were less expensive.  So we got a scale that was Half of O scale, HO scale for short.

What is HO scale, anyway?  Well, that depends on who you ask!  In the United States the National Model Railroad Association defines HO scale as:  1:87.0857142 usually rounded off to 1/87.1.  Why such an unusual number?  It is supposed to represent a ratio of 3.5 millimeters to one foot.  In Europe HO scale is 1:87.  That is all subject to change because many manufacturers and countries interpret HO scale differently.  In the UK they use OO.  Which is 1/76 scale.

However…There are two other factors to consider.  Scale is the ratio between the real object, the tank, train, aircraft, and the model tank, train, aircraft.  So 1/87 means a real aircraft with a wingspan of 87 feet would result in a model with a wingspan of one foot.

But in model trains it’s not the scale that is the most important factor; it is the gauge of the rails.  How far apart are the rails on a model train track?  The rails have to be a consistent and precise distance apart so that the model trains will fit and run properly on the model rails.  Operation of the railroad is more important to model train collectors than the precise size of the train models themselves.

To accommodate this need to run the trains European HO scale, American HO scale and United Kingdom’s OO all operate on the same train tracks; the rails are set 16.5 millimeters apart from one another.  In model railroad circles they will often talk about HO gauge rather than HO scale.

Standard HO gauge 16.5 millimeter wide railroad train track


n miniature wargaming, the miniature soldiers are described based on the height of an average soldier.  So standard size army men are two and a half inches tall, and they are often referred to as 54mm size or 1/32nd scale.  This is also an imprecise measurement because some manufacturers measure from the bottom of the base to the top of the helmet, and others measure from the bottom of the foot to the center of the eye socket!  On the theory that the top of the head may be covered by a hat but the eye socket should be visible.  So, again different manufacturers will have different size soldiers.  HO gauge, 1/87 scale figures should be 18.5mm size, measured from bottom of foot to center of eye socket.


HO gauge are train track rails set 16.5 millimeters apart;

HO scale is either 1/87 or 1/87.1 of the actual size of the object;

HO size is 18.5mm!

The important thing about HO model building is that the models look right to the observer.  It’s like that old question, how long is a piece of string?  How tall is a person?  How large is a building?  How high is a tree?  This gives tremendous freedom to the model builder because you can take HO scale as a guideline rather than a precise measurement, if you wish.

Airfix HO/OO First Series USMC figure with an O gauge Plastruct hospital building.  Public buildings are often built to a monumental scale and so humans look small next to them.


Your train layout, or wargame table, or diorama can mix items of different gauges, separate scales, and conflicting sizes if they are carefully selected.  Buildings as small as 15mm and as large as 28mm can look just right with HO scale tank models, provided the doors and windows on the buildings look right for the type of structures.

Large public buildings, like city hall, or a library may have doors ten feet tall or windows that open into a grand two story size room.  So select them carefully and you can mix and match items to suit your requirements.

Figures are often over scale and under scale, even from the same manufacturer!  Mixing scales of humans can be helpful to achieve variety so there are young and old people represented who might be smaller than young, fit military men.  Soldiers tend to look larger because they wear big boots and headgear and baggy uniforms with big packs. 

You can select figures that can be as small as 15mm or as large as 1/72nd scale in plastic, often cited as 20mm when made of soft metal.  Remember HO scale being 18.5mm is between those scales.  Sometimes you can find a range that is a little big for 15mm or a little small for 20mm and they can fit just right for your collection of HO vehicles.


Airfix HO/OO First Series German Afrika Korps figures with Roco Minitanks HO scale SWS Halftrack with 37mm gun Z-137 and Sturmgeschutz III z-177


In the early 1960s, the popular Roco Minitanks range of HO scale vehicles were widely sold by many retailers in the United States alongside the HO/OO scale boxes of Airfix soft plastic figures.  Thousands of young boys got their start in miniature wargaming using these vehicles and figures in backyards, sandlots, and living rooms.  Many of them still continue in that tradition of soft plastic figures in 1/72nd scale and HO scale vehicles.  Now, fifty years later the number of new HO scale military models has increase to phenomenal quantities and in complexity for every skill level to satisfy the most discerning eye!


 Roco Minitanks and Airfix figures fight a war that has lasted over 50 years!