Scales and gauges: choosing between Z, N, TT, HO, O and G

Model trains come in several sizes. The common ones are Z, N, TT, HO, O and G. This article covers the scale and track gauge of each, how big the models actually are, how much room they need, who each size suits, and where most beginners start.

Two words to keep apart: scale and gauge

Scale (German: Maßstab) is how much the model is shrunk compared with the real train. 1:87 means 1 mm on the model stands for 87 mm on the real thing.

Gauge (German: Spurweite) is the distance between the inner edges of the two rails, in millimetres. Whether a model can run on a given track depends on the gauge.

The two go together. Real standard-gauge track is 1435 mm wide; shrink that by 87 and you get about 16.5 mm, which is why HO track is 16.5 mm ¹⁵.

European standards bundle both into a single label called the nominal size (German: Nenngröße). Saying "H0" means 1:87 scale and 16.5 mm gauge at the same time ¹.

The six common sizes compared

The figures below follow the European NEM 010 standard and the American NMRA standards. Where the two differ, the table says so ¹².

\* These two columns are rough conversions (real size divided by the scale), not official figures. They are only there to give you a feel for the size.

The tightest curve radius decides how much floor a simple loop of track needs: the circle is about twice the radius across. From the table, a circle is roughly 30 cm wide in Z, 50 cm in N, 72 cm in HO and 1.2 m in G (an LGB R1 circle is 1200 mm across ²²). In practice you also need room for the width of the track and the overhang of the cars, plus some margin.

Who each size suits

The "who it suits" notes below are the editor's summary based on the sizes above and how popular each scale is. They are suggestions, not rules from any standard.

Z (1:220): the smallest, for very tight spaces and miniature scenes

Märklin launched Z in 1972 under the name mini-club. It is one of the smallest commercial scales on the market ⁷¹³. You can fit more track into the same area ⁷, but the market is small and the range of products is limited ⁷. The models are tiny, so putting them on the track, cleaning them and fixing them takes steady hands and good eyes.

N (1:160 / Japan 1:150): the first choice when space is short

N is second only to HO in popularity and is the most popular scale in Japan ⁶. Märklin also calls N the second-largest segment of the model railway market ¹². N models are roughly half the size of HO, so the same area holds a much longer run of track ⁶.

Japanese-outline N models are made to 1:150, except Shinkansen bullet trains, which use 1:160 ¹⁴. Most Japanese railways run on narrow 1067 mm gauge, and 1:150 keeps Japanese models from looking much smaller than European and American ones; that was the reason for choosing it ¹⁴. Both scales use 9 mm track, so they run on the same rails, but side by side the car bodies differ in size.

N couplers were historically standardised on Arnold's Rapido design. Arnold let other manufacturers use it, so cars from different brands can usually be coupled together ⁶.

TT (1:120): between N and HO, more common in Central Europe

The name TT comes from "table top" ⁸. It started in the US but became popular mainly in Central Europe, especially the former East Germany ⁸. Tillig is currently the largest TT maker, and most TT track on sale is made by Tillig ⁸. TT has picked up again in recent years: Piko and Roco make TT models, and Hornby in the UK launched its TT:120 range in October 2023 ⁸. If you mainly want German, Czech, Polish or other Central and Eastern European trains, TT is worth a look. For Japanese or American trains the choice is much smaller.

HO / H0 (1:87): where most beginners start

HO is the most popular model railway scale in the world ⁵ and the main scale in both continental Europe and North America ⁵. Most of Märklin's products are HO too ¹². Because so many people model in HO, there is a huge range of models, kits and supplies ⁵, and the second-hand market is the largest as well (the editor's inference; no figures found). English Wikipedia describes HO as a balance between detail and space ⁵: the models are big enough to handle easily and show their detail, and the smallest loop takes about 72 cm by 72 cm.

O (1:43.5 / 1:45 / 1:48): large models that need a room of their own

O is one of the oldest scales; Märklin introduced it around 1900 ⁹. From the 1930s to the early 1960s, three-rail AC O gauge toy trains such as Lionel were the most common kind in the US ⁹. The scale depends on the region: 1:43.5 in Britain, 1:43.5 or 1:45 in continental Europe, and 1:48 in the US, but the gauge is about 32 mm in all of them ¹²⁹. The models are big and have real weight in the hand. O suits people with a dedicated room who like large, detailed models.

G (45 mm gauge, several scales): garden railways

G is not one fixed scale. It covers large models that run on 45 mm track, at scales including 1:22.5, 1:20.3, 1:29 and 1:32 ²¹⁰. The "G" comes from the German word groß, meaning big ¹⁰. The best-known G brand is LGB (Lehmann Groß Bahn), launched in 1968 ¹⁰¹¹ and owned by Märklin since 2007 ¹¹¹². LGB builds European metre-gauge (1000 mm) trains at 1:22.5 ¹¹; under the European standard that combination is called IIm rather than a size of its own ¹.

G is often used for outdoor garden railways because the models are large and tough, and brass track stands up to sun and rain ¹⁰¹². Even the tightest LGB curve has a 600 mm radius ²²²³, so G generally does not fit on a desk indoors.

Which size should a beginner pick?

The editor's suggestions:

• If you have room for a board or table of about 1 m × 2 m, choose HO. It has the most modellers and the most products ⁵, which makes help easy to find and second-hand models easy to buy.
• If you live in a flat and only have a desk or a shelf, choose N. The same space holds far more track than HO ⁶, and N is the second most popular scale ⁶¹². If you want Japanese trains, N is the obvious choice, since it is the most popular scale in Japan ⁶.
• Leave Z, TT, O and G until you know what you want (extreme miniaturisation, Eastern European trains, big models, or a garden line).

The "1 m × 2 m" figure is the editor's estimate: an HO loop about 72 cm wide plus some room for sidings and margin. It is not a standard figure.

HO and H0: two spellings

HO and H0 are the same size. The name means "half O", because 1:87 is roughly half of O ⁵. The European NEM standards write H0 with a zero, read "H-zero" (in German, "ha-null") ¹⁴⁵; the American NMRA and the English-speaking world write HO with the letter O ⁴. When you search German or Japanese second-hand sites, try both spellings.

European NEM and American NMRA: the short version

• NEM (Normen Europäischer Modellbahnen, the European model railway standards) are maintained by MOROP, the European federation of model railway associations. The NMRA is the National Model Railroad Association of the United States ¹³.
• For the main scales and gauges the two agree: Z, N, TT and HO use the same figures ¹².
• O scale differs: NEM uses 1:45 (1:43.5 in some countries), the NMRA uses 1:48 ¹².
• HO is written with different precision: NEM says 1:87, the NMRA says 1:87.1 (3.5 mm to the foot) ¹²⁵.
• Narrow gauge is named differently. NEM adds a letter to the nominal size: m for prototype gauges from 850 mm up to 1250 mm (typically 1000 mm metre gauge) and e for 650 to 850 mm (for example 750 or 760 mm) ¹. The NMRA adds "n" plus the prototype gauge in feet, so HOn3 means a 3 ft prototype gauge, modelled on 10.5 mm track ². Both model narrow gauge of around 3 ft, but European H0m uses 12 mm track and American HOn3 uses 10.5 mm, so they don't mix ¹².
• The NMRA itself notes that sizes such as II are maintained by MOROP in the NEM standards ³, and NEM points to the NMRA standards for gauges and sizes that are uncommon in Europe ¹.

Same scale, different gauge: HOm and HOe

Many real railways are narrower than standard gauge (1435 mm). Models show this with a suffix after the size: H0m is a 1:87 metre-gauge train on 12 mm track, and H0e is a 1:87 train of the 650 to 850 mm class (for example 760 mm) on 9 mm track ¹⁴⁵. So an H0e train runs on the same 9 mm track as N, but its body is HO-sized.