Scale & Gauge

Discuss park gauge trains and large scale miniature railways having track gauges from 8" to 24" gauge and designed at scales of 2" to the foot or greater - whether modeled for personal use, or purpose built for amusement park operation or private railroading.

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Loco112
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Scale & Gauge

Post by Loco112 » Sat Dec 31, 2016 5:01 am

Scale & Gauge

Scale and gauge seem to be confusing for some, so I'll see if I can explain a few ways to figure them out.

Lets start with the track gauge you want to build for your miniature RR. (example) 15"

Whats the track gauge of the prototype you want to replicate in miniature? lets say you are into the Mountain rr's that use a 3' gauge. So well go with: (example) 36"

Put those two numbers together, as a fraction, with your small trains gauge on top and your prototypes gauge on the bottom, and you get 15/36. Divide 15 by 36 and you get .4166666

.4166666 is the same as: 5/12 , 5" to 12", 5" to the foot, and 5" scale .

So to replicate a 36' gauge trains for 15" gauge, the exact scale of your miniature is an even & exact, 5" scale.


Not all scales and gauges come out as nice round and even numbers. Heres our next example:

If the trains you want to model is a standard gauge train, like the ones we see rolling around the big cities of the USA, the track gauge of those is 56 +1/2" .

So if I wanted to build a miniature to run on the very common grand scale gauge of 15" track, I would put 15" over 56.5" and it would look like this: 15/56.5 Divide that fraction to get the a decimal figure, and you get about .2654867 which converts to a tiny fraction under 3.2" scale, 3.2" / 12", or 3.2" - 1' . .


If you know what scale you want to build to, you can figure out the scale you need to use to go with that track gauge, hers our next example:

Lets say you know you want to build to the traditional scale of 5" scale (5" - 1', or 5" - 12"). You also know the track gauge of the trains you want to use as your prototype, lets say you want to model standard gauge trains, so your prototype gauge is 56.5" .

You put the scale you want to build to as a fraction, so in this case its 5/12 and then convert that into a decimal, which is .41666666 Multiply that decimal times your prototypes tracks gauge, ( 56.5) and you get the scale miniature gauge in inches, I got 23.54"

(No one likes to builds to an uncommon track gauge, 23.5" is a rare track gauge,so most people would go up to 24" even inches because its more common. So to fit that slightly larger 24" gauge you would need a scale that was closer to 5.1/12") or you could still build to true scale of 5" but, you'd then have to widen some of the parts to get your wheels wider than the 23.56" that 5" scale is calculated to. The widening of those parts might be more complicated than building to 5.1" over the more common scale of 5" scale.
That is the decision you have to make when your scale and gauge do not come out to even numbers.

Gauge is the number you want to be very common, that's so others can visit your track or you can visit theirs.

Scale can be anything and it wont effect much. In our larger than commercial live steam scales, we build everything anyway, so the scale is insignificant to me.

When we talk about flanges and "back to back", that's when scale becomes very important.

I Hope this helps someone in figuring out what size, scale and gauge they want to build in.

There is a "Scale and Gauge" chart located inside Steve Booth's book: "Master Railroad Builder" that is very useful for estimating or figuring scale and gauge. It might already be in an old post. ??
Narrow Gauge (Information) Exchange dot Org forum
My Projects:
Davenport 30 ton diesel (SV#101 / D&RGW#50)
C&S 1908 steel & 1905 wood: box, stock, flat, gon
D&RGW wooden freight cars, long & short cabeese
EBT 2-bay hoppers, Conoco #44 tank
DV (K&J) hopper
8"n3 - 3-footers, 8" scale, 24" gauge

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