Scale and Gauge Encyclopedia
Scale and Gauge Definitions
The Scale/Gauge Encyclopia is my attempt to list all the model
railway scales that have been used over the past 125+ years, and
to list all the different names used to describe them. Further,
a modeler can chose to create representations of railways that
ran on different gauges of track in any one of these scales,
leading to an explosion of scale and gauge combinations -- more
than 1250 combinations are listed in this Encyclopedia.
To create the Encyclopedia, I read every issue of Model
Railroader (and its predecessor), Narrow Gauge and Shortline
Gazette (and its predecessors), Garden Railways, Finescale
Railrtoader (and its predecessor), as well as a number of older
hardcover books on model railroads, and the existing NMRA
Standards. I kept a record of every scale and gauge combination
mentioned in articles and advertisememts and built a spreadsheet
to keep the list organied. Like most model railway projects, it
just grew and grew, and continues to do so today.
There have been long standing differences between the practices
in Britain, Europe, and North America that can cause major
confusion in terminalogy, scale ratios, and usage of particular
track gauges. Over time, these have been clarified with
the help of the Internet and Wikipedea.
I have modeled railways in several scale and gauge combinations
across 70 years. I love model railways. I love the variety
of styles, eras, and sizes that are modeled. I hate the commercial
emphasis, especially by a few narrow-minded magazine editors, on just a few
modeling scales (N, HO). There are magazines and websites that
cater to many of the other available scales, so do search for what
might appeal to you.
IS IN THE ENCYCLOPEDIA?
The Encyclopedia consists of 7 webpages containing
Definitions (this page),
five Scale/Gauge Tables covering
scales that can be generically described as
all, there are 64 scales listed and more than 1250 scale and
gauge combinations that have been or could be used to represent
a model railway.
A sample of the Encyclopedia page for S Scale (1:64
Many of the scale/gauge combinations are merely different names
for the same combination, but each is listed to make it easier
to search for the obscure name or phrase. Many scales also have
multiple names and these are listed as well.
Each Scale Table has a header that contains the primary Scale
Name and the Scale Ratio, as well as Alternate Scale Names and
sometimes a pronunciation guide, if the name is a series of
The body of each table contains columns with the Table Number,
Serial Number, Gauge Name, the Prototype Gauge represented by
this Gauge Name (inches), Scale Ratio, Inches per foot and
Millimetrs per foot for this Scale Ratio, followed by Minimum
and Maximum model track gauge in inches and millimeters. If
there is no maximum, it means that no standards have been
published for this track gauge. This is followed by an Error
column and a commercial tarck gauge that could be used to
represent this gauge.
The error column represents the percent difference between the
correct gauge and the actual dimensions used to manufacture the
track. A negatibe error means the track is too narrow; positive
means the track is too wide.
Some of the words used in the foregoing may be unfamiliar. The
following section provides the definitions you might need.
and Gauge DEFINITIONS
confusion surrounds model railway scales, the names given to those
scales, and the various track gauges that can be modeled in each
scale. Let's review all the necessary definitions and possibly
some of that confusion can be cleared up here.
is a word used to mean the original, full size item that is to
or SCALE RATIO is the ratio in size between an original and a
model of the original. A very popular scale ratio for model trains
and model cars is 1:87, which means that the model's dimensions
are 1/87th the size of the original. This translates to 3.5 millimeters equals
1 foot. The Scale Name given to this Scale Ratio is "HO", each
letter pronounced separately as "aitch-oh".
This ismy 1:1 scale (full-size)
of Denver, South Park and Pacific Railway waycar #60.
It is a model of a prototype that ran back in the 1880's. ==>
It's hard to image the size of the prototype compared to a model
unless you put them side-by-side. Here's an example.
<== My full size caboose with a 1:20 or "F" scale train running
along the bottom edge. The little caboose on thee left end of
the short train is 1/20th the size of the full size caboose. An
HO scale train would be about 4.5 times smaller again.
or TRACK GAUGE is the distance between the rails of real or
modeled railway tracks. On the illustration at the right, the
TRACK GAUGE "G" is the distance between the inside edges of the
rails. On a standard gauge railway in North America that
distance is 56.5 inches. In HO Scale, the distance is 1/87th of
that or 0.649 inches (16.5 millimeters). The gauge specified is
usually the minimum allowed for safe operation and tolerances
are gfiven to indicate the maximum distance allowed.
COMBINATION is a track gauge used with a particular model scale.
The same gauge of model track can be used in several scales to
represent different gauges in these various scales. For example,
1-3/4 inch (45 mm) gauge track is used to portray many gauges
in many scales.
NAME is the word or abbreviation used as a shorthand label to
identify a model's scale. A scale of 1:87 is called HO Scale.
Some scales have many names; some have more than one scale ratio.
NAME is the word or abbreviation used as a shorthand label to
identify a model track gauge. For example, a track gauge of 1-3/4
inches (45mm) is traditionally called Gauge 1, but could be called
Fn3 if it was used to represent 3 foot narrow gauge in F Scale.
There is a phenomenal variety of names used for the same gauge.
railway rolling stock model is not fully described unless both SCALE and GAUGE
are specified. A railroad structure like a station or a water
tank is fully described by its scale only, as there is no tracck
Unfortunately, some SCALE NAMES are used to represent
more than one SCALE RATIO. For example, O Scale can mean any one
of four scale ratios. This is really confusing, even to experts.
make matters difficult, there are more than 60 different scales
in use today for model railways. Not all scales are equally popular,
and some are more popular in Europe or Britain than in North America.
Some are exceedingly rare and never seen except in old magazine
more confusion comes from mixing the words SCALE and GAUGE. For
example HO is the name of both a scale (HO Scale) and a gauge
(HO Gauge) of model train track. Some writers use the word GAUGE
when they mean SCALE, and vice-versa.
name like HOn3 is often called a SCALE but is, in fact, a GAUGE
of track, namely 3 foot NARROW GAUGE, modeled in HO SCALE. Even the National
Model Railroad Association (NMRA) fails to make the distinction
in their Standard S-1 and related documents.
advertizing copywriters, and editors have a collective amnesia
about perfectly good names that have been used in the past, and
insist on inventing new names. This is usually done without regard
to any established conventions or naming rules.
that have small ratios are called LARGE SCALES (eg. 1:20), because
the models are quite large, and SMALL SCALES have large ratios
(eg, 1:160). The breakpoint between large and small is usually
at about 1:40 scale.
most common commercially available scales for model trains in
North America are named
Z (1:220 ratio), N (1:160), HO (1:87), S (1:64), O (1:48), and
G (1:22.6+/-) scales. G Scale is only one of seven so-called “Large
Scales” that have scale ratios running between 1:13.5 and
1:32. The illustration below, showing the head-on view of a modern
diesel, illustrates the relative sizes of these scales. Note that
the illustration on the screen is about one-half actual size.
HO locomotive ahown above would be a little more than 1 inch wide and the
G scale locomotive would be about 4-1/4 inches wide.
In the background, a 1:20 scale locomotive (22.5 inches long),
in front of it is a 1:24 scale model of the same locomotive (18.75
inches long), and at the bottom right, an HO scale model of the
same locomotive (5.0 inches long), all of them a DSP&P 2-6-6T
Mason Bogie locomotive of the 1880's. These are 3-foot narrow
gauge steamers, so they could be called Fn3, Hn3, and HOn3 gauge
All four of these models are 28 foot 3-foot narrow gauge
boxcars. At the rear is a 1:22.5 "G" Scale model. It can be used
in 1:20 and 1:24 scales and no one would notice the fact that
the car was not exactly 28 feet long. The Gorre and Daphetid car
represents a 1:64 "S" Scale version. In front of that is a 1:87
HO Scale version and a 1:160 "N" scale car. If the G Scale car
was painted for a Standard Gauge railroad, it would represent a
36 foot old-time boxcar in 1:32 "1" Scale. The G&D boxcar is
actually a 36 foot HO standard gauge car, "standing-in" as an S
Scale narrow gauge car for this photo.
SCALES and GAUGES can be used in model railroading for several
reasons. A mix of standard and narrow gauges using a common
scale is the usual situation. It mimics real life railroad
scenes where two railways of different gauges meet and
interchange shipments. It can lead to DUAL GAUGE TRACKWORK,
which can be complicated and interesting to viewers and
operators of the model trains.
Using a much smaller scale for track, trains, and buildings can
simulate an amusement park ride for children and adults. I used
an N Scale train on my indoor G Scale railway for this purpose.
A real life garden railway built at 1:20 scale could use a Z
Scale model train to represent a garden railway in the back yard
of a model home.
Finally, using the next smaller scale on trains running in the
baclground can be used to enhance the sense of distance by
tricking the eye with forced perspective. I did this by using an
O Scale train on a "distant" mountain on my G scale layout. You
can translate these concepts easily to smaller scale model
railways in HO, S, and O Scales. Smaller scale buildings,
vehicles, and trees in the background can be used in the same
way to expamd the horizon.
The yellow train in the upper background is O Scale (1:48) while
the yellow train in the middle foreground is G Scale (1:22.5).
The two trains are only 12 feet apart, but the sense of distance
is much larger.
A 1:22.5 Scale passenger train pauses at Tiny Town to drop off children
to ride on the 1/8 scale
"live-steam" train (N Scale) that circles the 1/8 scale grain elevator and
Mixing rolloing stock from different Scales in the same train
can look strange when the sizes are too different. This
happens most often in the large scale environment where 1:32 and
1:29 Scale standard guage trains can run on the same physical
track as 1:20 or 1:22.5 Scale narrow gauge trains. When an
old-time steam engine is ohysically bigger than a modern diesel,
the sense of realism is broken.
LENGTH is shorter than prototype length by a factor equal to the
SCALE RATIO. The equation is:
Scale length (feet) = Prototype length (feet) divided by SCALE
For example: a 40 foot boxcar in O scale would be 40 feet times 12
inches / foot / 48 = 10 inches.
Scale track gauge (inches) = Prototype track gauge (inches) divided
by SCALE RATIO
For example: standard gauge track (56.5 inches) in O scale would be
56.5 inches / 48 = 1.77 inches.
Scale track gauge (millimeters) = Prototype track gauge (mm) divided
by SCALE RATIO
For example: standard gauge track (56.5 inches) in HO scale would
be 56.5 inches times 25.4 mm / inch / 87
= 16.5 mm.
AREA is smaller by a factor equal to the SCALE RATIO squared,
and SCALE VOLUME decreases by a factor of the SCALE RATIO cubed.
a mile of track at a scale of 1:87 is 5280 feet divided by 87,
which equals 60.68 feet. A scale square mile of land would be
about 61 by 61 feet, which is much larger than most model railways.
That's why we use SELECTIVE COMPRESSION to pack a meaningful scene
into a small space on a model. For example, a typical paved 2-lane
highway is 100 feet wide between fence lines. This is 13-3/4 inches
wide in HO Scale. We can't afford to give up over a foot of space
for a highway on a model, so we selectively compress it to less
than 6 inches. The eye usually doesn't mind.
WEIGHT is proportional to volume, so the weight of a 100 ton locomotive,
at 1:87 scale, would be: (100 tons x 2000 lb/ton x 16 oz/lb) divided
by (87 x 87 x 87) = 4.86 ounces. This would be far too light to
operate; the average model locomotive at this scale weighs 10 to
20 ounces. Unfortunately, we can't model the pull of gravity.
SPEED equals actual speed multiplied by the SCALE RATIO. A model
traveling 20 feet per minute is moving at an actual speed of 0.227
miles per hour, equivalent to almost 20 scale miles per hour in
HO Scale (1:87). Most models travel too fast; the worst being
run at over 300 scale miles per hour. The conversion equation
Scale Speed (mph) = 1/88 times Speed (feet/minute) times SCALE
people use a SCALE MILE (often called a Smile) which is shorter
than a real scale mile, and others use SCALE TIME, usually 5 to
10 times faster than real time, to account for selective compression
of model railways and the high speeds of model trains. Here, Scale
speed (sph) = Smiles divided by Scale time.
tables were created on a spreadsheet, using these
inch = 25.4 mm exactly
meter = 3.281 feet exactly
= 12 / (inches/foot)
= 12 / Ratio
= 12 / (mm/foot) / 25.4
= 12 * 25.4 / Ratio
= 1000 / (mm/meter)
= 1000 / Ratio
track gauge (inches) = Prototype gauge (inches) / Ratio
track gauge (mm) = 25.4 * Prototype (inches) / Ratio
Error To Prototype = ((Model track gauge * Ratio / Prototype
gauge) - 1) * 100
= model tracks are too wide,
= model tracks too narrow.