What is S-scale?

The Basics

"S" was the name given by the National Model Railroad Association (NMRA) in 1943 for modeling in a ratio of 1:64. Meaning, real-world (a.k.a. prototype) measurements are divided by 64 to provide the scale model dimensions. The scale is also known as "3/16th scale", because a prototype English foot is equal to 3/16th of an inch in S-scale. Conveniently, each 1/64" tick mark on a ruler represents one scale inch on the model.

"S" vs. Other Scales

S-Helper Service S-scale vs. Micro-Trains N-scale PRR box car
© Peter Vanvliet; used by permission

S-scale sits at about the middle of all the other popular model railroading scales. It is 25% smaller than the next larger O-scale (1:48), and it is 36% larger than the next smaller HO-scale (1:87). It is exactly two and a half times bigger than N-scale (1:160). S-scale is half the size of the original Gauge-1 scale (1:32) (garden scales have various ratios all using the same 45mm-wide track).

Many people consider S-scale to be the perfect model railroad scale, because it doesn't take up much more space than HO-scale, but it does provide the heft needed in locomotives to make them run better. As modelers get older, the fine details in N- and HO-scale modelers may become harder to see, and working in those scales may become more difficult. S-scale makes working on your cars and engines much more fun. The larger O-scale and G-gauge would make working on those details even easier to see, but because those details are clearly visible, they almost have to be modeled. This makes modeling in those scales a lot of work. Further complications ensue when dealing with multiple or larger motors inside those engines, or with wanting to build full-size structures in our limited spaces.

S-scale has also been called the "builder's scale". This used to be very real in the early days, but much less so today. Many items are available ready-to-run, or in kits that are easy enough to build. Nevertheless, if you enjoy building, "S" is a good scale to be in.

Ultimately, if you are interested in the hobby of model railroading, it is an individual decision as to which scale to use. We feel that S-scale just looks right to the eye, and, from those who have switched from N- or HO-scale, the feedback has consistently been that it is much easier to build things in S-scale, from track to structures and even scratchbuilding cars and engines.

The photo below is a great shot of comparing a similar 40-foot box car across the various scales.

© Bill Lane; used by permission

Scale vs. Gauge

Throughout this web site we refer to modeling in 1:64th scale as "S-scale". You will find magazines and other web sites using the term "S-gauge" or "S gauge". That terminology is not correct. That terminology has its roots in the early days of when the model railroading hobby started. You will find similar terminology used in other scales as well (e.g. "N gauge"), so this is not an S-scale-only problem.

The word "gauge" refers to the distance between the rails (standard-gauge vs. narrow-gauge), while "scale" is the ratio of prototype size to the modeled size (e.g. 1:64). So, other than for legal or historical reasons, we will always use "S-scale" on this web site. Yes, post-war American Flyer is "S-scale".

Past NASG presidents Roy Hoffman and Bill Winans have publicly expressed that we should start to use the term "S-scale" instead of "S gauge".

In the photo below, note how the volume of the On3 car (back row, center) is almost the same as the S standard-gauge car (middle row, left), and how the HO standard-gauge car (front row, left) is almost the same as the Sn3 car (middle row, center).

back row: O, On3, On2; middle row: S, Sn3, Sn2; front row: HO, HOn3, HOn2
© Dave Heine; used by permission

American Flyer, Hi-rail, and Scale

An A.C. Gilbert American Flyer-style Layout
© Peter Beckerle; used by permission

S-scale has its roots in the American Flyer brand. Before World War II, A.C. Gilbert bought the American Flyer product line, and made trains that could operate on the Lionel O-scale track. The equipment was made to 1:64 scale, but the wheels and trucks were gauged to the wider O-scale standard. After WWII, to be able to better compete with rival Lionel, A.C. Gilbert developed the more prototypical-looking two-rail system, and spaced the rail gauge to that of S-scale. Lionel, in its O-scale track, uses a third rail down the center of the track, since it primarily used AC power for the engines. A.C. Gilbert won the battle of which of the two had the most realistic-looking track.

A Hi-rail Layout (hi-rail wheels and track, scale couplers)
© Brooks Stover; used by permission

There are four distinct groups within the S-scale community, namely "American Flyer" (typically abbreviated as "A.F." or "AF", sometimes also called "tin plate" especially when referring to pre-war items), "hi-rail", "scale" (usually referring to standard-gauge track), and "narrow-gauge". All model in S-scale, or the 1:64 ratio, but with some slightly different flavors. Because of the American Flyer roots, there are a lot of people who still have and perhaps operate original A.C. Gilbert American Flyer products. Lionel now owns the American Flyer brand name, and they continue to manufacture products under that name. These are compatible with the older A.C. Gilbert A.F. products. "Scale" modeling covers both standard-gauge and narrow-gauge. This is similar to the popular HO-scale. Models have finer details and are more delicate.

A Scale Layout
© Bob Werre; used by permission

The significant difference between A.F. and scale is that A.F. uses the larger knuckle coupler, deep-flanged wheels, and the wheel thread is wider in AF. The couplers are incompatible with Kadee-style couplers used by scale modelers (but can generally be swapped out fairly easily). The AF deep-flanged and wider wheels will, generally, run on straight or curved track, if the rail height is tall enough. However, due to the wider width of AF wheels, they will not operate on "scale" turnouts. However, "scale" wheels should operate just fine on AF or "high-rail" turnouts. "Scale" wheels and trucks are available and can be used to replace AF trucks, if so desired. AF modelers usually also enjoy the A.C. Gilbert style of accessories, such as animated structures and signs. The "hi-rail" group of modelers fit in between true AF modelers and true scale modelers. These are usually people who started off with American Flyer and are slowly transitioning to more scale-like modeling.

The modeling style is an individual choice; whatever gives you the greatest enjoyment out of this hobby. After all, that is the objective of a hobby. All "flavors" of S-scale modeling are actively supported within the S-scale community and by the NASG and on this web site. The "united" word in the NASG logo refers to the fact that we are all still 1:64-scale modelers.

As a side note, lest you think these issues are unique to S-scale only, N-scale used Rapido couplers that are incompatible with the Micro-Trains or Kadee-style couplers, as well as deep-flanged wheels; HO-scale used to have the old horn-hook couplers that are also incompatible with Kadee-style couplers; O-scale is very similar to S-scale, in that it, too, has claw-style couplers that are incompatible with Kadee-style O-scale couplers and deep-flanged wheels. Additionally, O-scale has the issue with their rail gauge being five feet wide, not the correct 4' 8-1/2", and they use a center rail to conduct electricity.

An Sn3 Layout
© Bob Hogan; used by permission

Modeling in narrow-gauge in S-scale is a lot easier than in the smaller scales. The engines track better. There is more space inside for DCC and sound. The details are easier to see. P-B-L is the main Sn3 equipment manufacturer. Sn2 is primarily supported by Portland Locomotive Works and Train & Trooper. Bar Mills, the structure kit manufacturer, has an Sn2 layout in the foyer of their business office, built by the owner Art Fahie and some of his friends. There are a few people who model in Sn42 (a.k.a. 3-1/2' gauge). Railmaster Exports is one manufacturer how provide locomotive kits (both steam and diesel). These are primarily intended for New Zealand, South Africa, and Canada modeling of 3-1/2'-gauge prototypes.

There is also a small group of S-scale modelers who use the Proto:64 standard for track and wheels. This standard uses an exact down-sizing of the real track dimensions. This requires very accurate track components and track-laying disciplines, and matching exact-size wheels on both locomotives and cars. There are a few companies that make Proto:64 parts. If done with the required accuracy, this will yield very realistic-looking track and wheels.

How to Get Started in S-scale

American Flyer Collector/Operator

A.C. Gilbert American Flyer #958 Tank Car
© Ted Hamler; used by permission

If you already have some A.C. Gilbert American Flyer equipment, and you wish to continue to expand your collection or to start operating (i.e. build a layout), your best choice is the secondary market (e.g. eBay, various discussion groups, clubs, consignment dealers, and estate sales). Rare items show that in their pricing, and common items should be easy to get. You will definitely want to get the Greenberg's American Flyer Pocket Price Guide published by Kalmbach every year (available at many retail stores, as well as online at places such as Amazon and Barnes & Noble). For track, if you want to remain pure A.F., you will have to, again, look at the secondary market. GarGraves makes track that looks like the original A.C. Gilbert track. However, if you are OK with getting more scale-looking track, you can buy new track from Lionel, MTH, Fox Valley Models, and American Models. On the secondary market you may also find some S-Helper Service track components (however MTH is making the exact same components now). For a complete listing of what is available, be sure to click on the S Resources button on the left.

If you are interested in building a layout that combines both original A.F. and the more newer products, you will want to look at locomotives and cars that are truly AF-compatible. All Lionel and MTH products are AF-compatible. Other companies, such as American Models, make equipment that can be ordered for scale- or AF-compatibility. You can buy the same track components mentioned above.

Scale Modeler

Scale Tank Car on S-Helper Service/MTH Track
© Ken Garber; used by permission

If you are a pure scale modeler, most of the A.C. Gilbert-era American Flyer (i.e. pre-1969) does not apply, unless you want to spend time converting the equipment. MTH (which bought the former S-Helper Service tooling) makes it easy to convert their AF-compatible equipment to scale. Couplers and wheels are sometimes provided in the box, and pre-drilled holes in the underframe for Kadee-style couplers are usually provided. Some retailers will even do the conversion for you, if so requested. You can order equipment from American Models in either "scale" or "AF-compatible" (be sure to look for "DC", i.e. direct-current, equipment; "AC" current is compatible with older AF-style layouts). Newer Lionel equipment is mostly convertible to "scale", but some items require more work than others. Their freight cars may be as easy to convert as MTH's, but if you buy a "hi-rail" (which is another term used to describe AF-compatibility) locomotive, the wheels come with deep flanges. These may require custom work (or replacement) to make them compatible with scale track. So, if you are looking at Lionel engines, be sure to check that they have scale wheels or that scale wheels can be bought separately, which is something Lionel has been offering on some of their engines since about 2012. There are also several small manufacturers that make S-scale equipment. Most of these usually default to making "scale" equipment, or they simply do not provide the trucks and couplers, so that you can choose for yourself.

Most modern S-scale engines use motors on par with HO-scale equipment. So, for DCC systems, you can treat S-scale engines as you would HO-scale engines. The motors will work with any DCC decoder on the market (sound or not) that is compatible with HO-scale equipment.


So, if you are interested in running any kind of American Flyer type of equipment, look for A.C. Gilbert items (pre-1969), or look for AF-compatible or "hi-rail" in the product description. If you are a scale modeler, look for newer products, and order them for "scale" or find out if the AF-compatible product can be converted to scale. Joining one of the discussion lists (A.F. or scale) is a good way to get your questions answered.

If you want to learn more about which track you might want to select, be sure to read through our Track Modeling Notes page (accessible via the Extra Board button on the right).

Currently, about 60-70% of the S-scale community fits within the A.F./hi-rail group, and about 30-40% are scale modelers. Outside of the track, wheels, and couplers, there is, of course, a tremendous overlap of other items such as structures and scenery items.

The whole purpose of the S Resources button on the left is to help find what is available to the S-scale modeler. Armed with the knowledge from the paragraphs above, you will be better able to figure out what style of modeling you would enjoy and which products you want to purchase to build your layout.

Want Some More Help?

One reason for the existence of the NASG is to bring people together who have a common interest in modeling in 1:64 scale. Whether or not you are an NASG member, the NASG's regional vice-presidents are here to help you with whatever questions you have. If they don't have the answer themselves, they certainly have the contacts to get you the info.

Contact the Eastern Vice President, Jeff English, if you live in Alabama, Delaware, Connecticut, Florida, Georgia, Kentucky, Maine, Maryland, Massachusetts, Mississippi, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, West Virginia, District of Columbia, Canada (Maritime Provinces, Quebec, Ontario), or Europe.

Contact the Central Vice President, Jay Mellon, if you live in Arkansas, Illinois, Indiana, Iowa, Kansas, Louisiana, Michigan, Minnesota, Missouri, North Dakota, Nebraska, Oklahoma, South Dakota, Texas, or Wisconsin.

Contact the Western Vice President, Peter Gehret, if you live in Alaska, Arizona, California, Colorado, Hawaii, Idaho, Montana, New Mexico, Nevada, Oregon, Utah, Washington, Wyoming, Canada (Alberta, British Columbia, Manitoba, Northwest Territories, Saskatchewan, Yukon), New Zealand, or Australia.

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