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Most model railroaders know this stuff, but I get a lot of e-mails from non-model railroaders. So rather than ignoring their questions or taking the time and effort to explain it over and over I decided to post a web page. And if you are a model railroader and I have directed you here SHAME ON YOU! You've asked me a question like how big is something (a model) in real life. Sorry, but it irrates me that you either don't have a scale ruler or the knowledge to convert the scale size to real life.

Where to begin? Soon after the first steam locomotive was invented no doubt some little kid was dragging around a board on a string imagining it was a locomotive and he was the engineer. We've come a long way since then and the little kids have grown up. It's now a mature hobby enjoyed by many adults. Early on they were just toys, in all shapes, and all sizes. Not much attention was paid to scale or accuracy. Eventually, certain toys caught on. Lionel's early standard gauge, then the O27. American Flyer stood their ground with something in the middle, 1/64th scale, which became known as S-scale. Lionel's O-scale wasn't exactly to scale with the locomotives and cars slightly smaller than the track's width would indicate. True O-scale is 1/48th scale. And the most popular HO scale 1/87th came out of Europe was derived from the odd mix of 3.5mm = 1 foot! Why didn't they choose something simple like 1/8" = 1 foot (1:96th)? It's all very confusing.

No matter why or how here we are with a handful of scales. Besides those in model railroading there are a bunch in other hobbies such as scale airplanes, model racecars, military models, war games, voodoo and doll houses. Please don't ask me questions about those. I don't know. I can only support the few I do. If something I have works for you that's great, I'm glad to share. But please don't ask me to figure it out for you or engineer YOUR project. I've got my hands full with the train stuff. But here are a few clues.

Here's a link to:   The National Model Railroad Association

They are sort of the traffic cops in all this, setting standards, and having fun.


Remember this number: 7.25. HO scale is 1/87th scale. So let's divide 87 by 12 which equals 7.25. So if we know let's say a box car is 40 ft. long we divide that by 7.25 to get roughly 5-1/2 inches. Yep, a 40 ft. HO scale boxcar is about that. And if we have a model that is 8 inches long we can multiply it by 7.25 and learn that it is a scale 58 ft.

I'll let you figure out what the magic number is for your scale.

Oh, I'll give you a clue if you are modeling On30. It is the same as O scale. Quarter inch anyway... Oh, forget it.


A European customer asked what are the metric equivalents to our scale feet? Heck if I know? But let's figure it out.

N scale is tiny. I don't even know what = 1 foot. It is 1:160 so 0.075" = a foot? Boy, I only do a few things in N-scale. Sorry, it's just not my thing.

And Z scale, forget about it! 1:220 or something like that.

When I was a kid my father brought me a tiny locomotive from Europe (British I think?). It was TT scale. Later on, well, I was still a kid, someone else gave me some additional pieces when they learned I was a model railroader. TT is something like half-HO scale. Sorry, I don't know exactly what. It's not supported in the US. I doubt it is truly half-HO but a little bit bigger or smaller. Similar is size N-scale won out.

HO scale by far is the most popular model railroad scale is the US. It was a popular scale in Europe. In 1959 or so I received my first model train set, an HO scale Lionel Santa Fe passenger set, for Christmas. I was one happy boy! Here nearly 50 years later I'm still at it.

HO scale is 3.5mm = foot. 1:87 So that's 12 divided by 87 = 0.1379" = 3.5mm

S scale is 3/16" = foot. 1:64 So 0.1875 = 4.7625mm

O scale is 1/4" = foot. 1:48 So 0.25" = 6.35mm

As I mentioned Lionel "O-scale" is a little smaller, 1:43 or is it 1:32? Something like that? Standard gauge? O27?? Sorry, I get confused. If it's not true 1/4" I don't really support it other than if it is close. If it works for you, great. If not, sorry. But you'll have to decide. Don't ask me. I didn't come up with these crazy scales or loose interpretations thereof.

G scale is another odd one with a bunch of nearby incarnations. There's true G scale 1:22.5 (one of those European conversions), 1/2" = 1 foot ( I think call that F scale), and others larger (1:20.3) and smaller (1:29). These all fit the category of "large-scale". I've got a handful of stuff that I generically call G-scale. It's just BIG stuff roughly double my O scale products. If you need something more exact to a particular scale you probably don't want my stuff. I just can't do everything for everyone. I can barely do HO scale for me!

To see how many scale inches something is divide by 12 (12 inches per foot) times however many inches you need to know, for instance 8 scale inches in O scale is 6.35mm /12 x 8 = 4.23mm.

So 36" in O scale is 19.05mm and 14.29mm in S.

This site should help with the conversions:   worldwidemetric.com


Most of my stuff is HO scale (unless otherwise noted) which is a ratio of 1:87. S-scale is 1:64. So we divide 64 by 87 to get 73.6 percent. HO scale is 73.6% the size of S-scale. So if something in HO scale is 10 feet it would be 7.36 feet in S-scale.

If you want to know how many real inches that is divide it by the scale (87) = 0.115 feet. Multiply that x 12 to get 1.379 inches. So ten feet in HO scale is a little over 7 ft. in S, and about 1-3/8 real inches.

I know, it's confusing as all heck. Get yourself a good scale ruler if not three or four.

  • for N scale reduce to 54.5% of original
  • for S scale enlarge to 135.7%
  • for O scale enlarge to 181% of original


C. C. CROW 's