Model train scales: HO, N, O, OO, G, Z and S ratios

HO gauge is 1:87.1 scale under the National Model Railroad Association (NMRA) Standard S-3.2 and 1:87 under NEM 010, the European model railway standard, both on 16.5 mm (0.65 in) track. The two ratios differ by about 0.1%, or 0.1 mm on a 100 mm model. The table lists every common model train scale, the height of a 1.73 m (5 ft 8 in) person at each, and the slicer percentage that shrinks a full-size (1:1) model to match.

Scale	Ratio	Track gauge	1.73 m person	Slicer % from a 1:1 file
Z	1:220	6.5 mm	7.9 mm (0.31 in)	0.455%
N	1:160	9 mm	10.8 mm (0.43 in)	0.625%
TT	1:120	12 mm	14.4 mm (0.57 in)	0.833%
HO	1:87.1	16.5 mm	19.9 mm (0.78 in)	1.148%
OO (00)	1:76.2	16.5 mm	22.7 mm (0.89 in)	1.312%
S	1:64	22.5 mm	27.0 mm (1.06 in)	1.563%
O (US)	1:48	1.25 in (31.75 mm)	36.0 mm (1.42 in)	2.083%
On30	1:48	16.5 mm	36.0 mm (1.42 in)	2.083%
O (Europe)	1:45	32 mm	38.4 mm (1.51 in)	2.222%
Gauge 1	1:32	45 mm	54.1 mm (2.13 in)	3.125%
G (LGB)	1:22.5	45 mm	76.9 mm (3.03 in)	4.444%
F (Fn3)	1:20.3	45 mm	85.2 mm (3.36 in)	4.926%

Ratios for Z through O (US), On30 and F come from NMRA S-3.2. O (Europe), Gauge 1 and the 1:22.5 size come from NEM 010. The person is 1,730 mm divided by the ratio: the average man’s height to the top of the head, per The Miniatures Page. The last column is 100 divided by the ratio.

Scale is the size of the model against the real train. Gauge is the distance between the rails. Each scale has a standard track gauge, so “HO gauge” and “HO scale” name the same models. The two split only where one track carries several scales, as it does for OO, On30 and G.

What scale is HO?

HO is 1:87.1 scale in the NMRA standard and 1:87 in Europe’s NEM 010, which writes it H0. HO trains run on 16.5 mm (0.65 in) track. NEM 010 calls HO 3.5 mm scale, and 304.8 / 3.5 = 87.09. A 1.73 m person is 19.9 mm (0.78 in) tall in HO.

HO track is true to scale. Real standard gauge is 4 ft 8½ in (1,435 mm), and 1,435 / 87.1 = 16.5 mm.

A foot is exactly 304.8 mm, per the US National Institute of Standards and Technology (NIST). A 40 ft car is therefore 12,192 mm long, and 12,192 / 87.1 = 140.0 mm (5.51 in) in HO. Printed from a full-size file, that is 1.148% in the slicer. To move an HO model to N, OO or O, the scale calculator has the railway presets and the percentages.

What scale is N gauge?

N gauge is 1:160 scale in the US and Europe, under both the NMRA and NEM standards, on 9 mm (0.35 in) track. British N models are built to 1:148 and Japanese ones to 1:150, on the same track. A 1.73 m person is 10.8 mm (0.43 in) tall at 1:160.

A 40 ft car at 1:160 is 76.2 mm (3.00 in) long. For a British N layout, use 1:148 instead: 0.676% from a full-size file, and a 1.73 m person comes out 11.7 mm tall.

What scale is O gauge?

O gauge is 1:48 scale in the US, a quarter inch to the foot, on 1.25 in (31.75 mm) track under NMRA S-3.2. Europe’s NEM 010 sets O at 1:45 on 32 mm track and notes that some countries use 1:43.5, or 7 mm scale. A 1.73 m person is 36.0 mm (1.42 in) tall at 1:48.

O variant	Ratio	Track gauge	1.73 m person	% from 1:1
US O scale	1:48	1.25 in (31.75 mm)	36.0 mm	2.083%
European O	1:45	32 mm	38.4 mm	2.222%
7 mm scale	1:43.5	32 mm	39.8 mm	2.299%
On30	1:48	16.5 mm	36.0 mm	2.083%

A 40 ft car at 1:48 is exactly 254 mm (10.00 in) long.

What scale are Lionel trains?

Lionel says most of its O-gauge trains are about 1:48. Its Traditional line only approximates 1:48 and typically runs on tight O-27 or O-31 curves. Its Standard O cars and engines are made as close to 1:48 as possible and often need O-36 or wider. The number is the diameter of a full circle of that track in inches: O-72 track makes a 72 in circle.

All Lionel O-gauge track, O-27 and FasTrack included, measures 1 1/4 in between the outer rails. Lionel also sells S gauge under the American Flyer name at about 1:64, G-gauge sets at about 1:24 and HO trains at 1:87. To print parts that match a Traditional Lionel car, measure it rather than assuming 1:48.

What scale is On30?

On30 is O scale (1:48) for modeling 30 in narrow-gauge railways, and it runs on 16.5 mm HO track. NMRA S-3.2 lists On30 under O scale with the same 0.649 in minimum gauge as HO. At 1:48, 30 in comes to 30 × 25.4 / 48 = 15.9 mm, so HO track is a close fit. Print figures and buildings for On30 at 1:48, not HO.

What scale is OO gauge?

OO gauge (also written 00) is 1:76.2 scale, 4 mm to the foot, on 16.5 mm (0.65 in) track. That is HO track under models 14% larger than HO, since 87.1 / 76.2 = 1.14. British ready-to-run OO comes mainly from Hornby and Bachmann Branchline. A 1.73 m person is 22.7 mm tall in OO.

Four millimeters to the foot gives 304.8 / 4 = 76.2. The track is too narrow for that scale. At 1:76.2, real standard gauge would be 1,435 / 76.2 = 18.83 mm. OO’s 16.5 mm track scales up to 16.5 × 76.2 = 1,257 mm (4 ft 1½ in).

Wikipedia traces this to early British models: motors were difficult to fit at HO size, so builders enlarged the bodies to 4 mm scale and kept HO track. The finer EM (18.2 mm) and P4 (18.83 mm) standards widen the track to match.

NMRA S-3.2 also lists an OO standard, 1:76.2 on 0.750 in (19.1 mm) track. That is American OO, which Lionel made on 19 mm track from 1938 to 1942. British OO uses 16.5 mm.

What scale is G scale?

G scale is not one scale. G is a track gauge, 45 mm (1.77 in), that carries several scales. NMRA S-3.2 lists 1:32, 1:29, 1:24, 1:22.5 and 1:20.3 as the large scales on 45 mm track, standard or narrow gauge. LGB builds most of its models at 1:22.5.

Ratio	Name	What it models	1.73 m person	% from 1:1
1:20.3	F scale (Fn3)	3 ft narrow gauge	85.2 mm (3.36 in)	4.926%
1:22.5	G, NEM IIm	Metre gauge; most LGB models	76.9 mm (3.03 in)	4.444%
1:24		3 ft 6 in gauge; Lionel G-gauge sets	72.1 mm (2.84 in)	4.167%
1:29		Standard gauge, first used by Aristo-Craft	59.7 mm (2.35 in)	3.448%
1:32	Gauge 1 (NEM I)	Standard gauge	54.1 mm (2.13 in)	3.125%

On the same rails, a 1:20.3 figure is 32 / 20.3 = 1.58 times the height of a 1:32 figure. Check the ratio of your trains before printing scenery or figures.

What scale are LGB trains?

LGB makes most of its models in size G, 22.5 times smaller than the real train, which is 1:22.5. The company says the size suits narrow-gauge models in particular and keeps small details sturdy enough for an outdoor garden railway. That matches NEM 010’s IIm: metre-gauge railways at 1:22.5 on 45 mm track.

What scale is Gauge 1?

Gauge 1 is 1:32 scale on 45 mm track, nominal size I in NEM 010, for standard-gauge railways. It shares 45 mm track with LGB’s metre-gauge models at 1:22.5, so the two run on the same rails at different sizes.

What scale is Z scale?

Z scale is 1:220 on 6.5 mm (0.26 in) track in both the NMRA and NEM standards, the smallest scale in either table. A 1.73 m person is 7.9 mm (0.31 in) tall at 1:220 and a 40 ft car 55.4 mm (2.18 in) long. From a full-size file, the slicer percentage is 0.455%.

What scale is S scale?

S scale is 1:64, or 3/16 in to the foot, on 22.5 mm (0.885 in) track under NMRA S-3.2 and NEM 010. In the US, Lionel sells S gauge as American Flyer: about 1:64 in its Traditional line and as close to 1:64 as possible in its S Scale line.

A 1.73 m person is 27.0 mm (1.06 in) tall at 1:64, and a 40 ft car is 190.5 mm (7.50 in) long.

How do you 3D print at HO, N or O scale?

Divide 100 by the ratio number for a model drawn at real size. That gives 1.148% for HO, 0.625% for N and 2.083% for US O. You can type the printed size in millimeters instead: real length divided by the ratio. A 2.0 m door is 2,000 / 87.1 = 23.0 mm in HO.

For a file already at another scale, the percentage is the old ratio number divided by the new one, times 100. The scale calculator has presets for Z, N, TT, HO, OO, S and O.

Tabletop figures overlap some train scales. Wikipedia’s miniature scale table gives these ranges:

Figure scale	Ratio	Train scale in that range
10mm	≈1:160 to 1:182	N (1:160)
20mm	≈1:72 to 1:90	HO (1:87.1), OO (1:76.2)
28mm	≈1:62 to 1:64	S (1:64)
35mm	≈1:48 to 1:52	US O (1:48)
54mm	1:32 to 1:35	Gauge 1 (1:32)
75mm	1:24	1:24 on G track

The miniature scale calculator converts between figure sizes.