Scales and gauges
They are different measurements and they do not always agree — which is why Britain runs 1:76 models on 1:87 track and nobody blinks. Here is the whole family, drawn to size on one page.
Scale is a ratio: 1:87 means the model is one eighty-seventh of the real thing in every direction. Gauge is a distance: the width between the inner faces of the two rails. Real standard-gauge track is 1,435 mm — 4 ft 8½ in — and at 1:87 that comes out at 16.5 mm.
George Stephenson used the wheel spacing of the Killingworth colliery wagonways, added half an inch of play, and won the Rainhill Trials with it. Most of the planet's railways are that width because his was first and everything after had to connect to it.
One 50-foot boxcar, drawn to size at each scale, all on the same page. Hover a button to pick one out. The numbers on the right are the model's actual length in your hand.
Practical minimum radius means “ordinary ready-to-run models will run reliably”, not “the tightest thing that will physically go round”.
| Scale | Ratio | Gauge | Min radius | Best for |
|---|---|---|---|---|
| Z | 1:220 | 6.5 mm | 195 mm / 7.7 in | Briefcase layouts and coffee-table dioramas. Limited range, high prices, and you will need good light. |
| N | 1:160 1:148 UK, 1:150 JP | 9 mm | 280 mm / 11 in | Long trains and real landscape in a bedroom. The best compromise if you want scenery to dominate. |
| TT | 1:120 | 12 mm | 330 mm / 13 in | Halfway between N and HO. Recently revived with strong European support; still a small catalogue. |
| HO | 1:87.1 | 16.5 mm | 450 mm / 18 in | Everything. The largest range of models, parts and second-hand stock on earth. |
| OO | 1:76.2 | 16.5 mm | 438 mm / 17.25 in | British outline. Slightly oversize bodies on HO-gauge track — see below. |
| S | 1:64 | 22.4 mm | 610 mm / 24 in | Big enough to detail, small enough to fit a room. Expect to build more than you buy. |
| O | 1:48 1:43.5 UK, 1:45 EU | 32 mm | 790 mm / 31 in | Presence and weight. A single O-scale locomotive on a shelf is a more satisfying object than a whole N-scale train. |
| 1 | 1:32 | 45 mm | 1.2 m / 4 ft | Fine-scale large modelling, live steam, and garden lines with generous curves. |
| G | 1:19 – 1:32 | 45 mm | 600 mm / 2 ft* | Outdoors. Survives rain, sun and cats. *Short four-wheel stock will take much tighter curves than long bogie stock. |
British models are built to 4 mm to the foot (1:76.2) but run on 16.5 mm track, which at that scale represents 4 ft 1½ in — about 7 scale inches too narrow. It happened because early motors would not fit inside a correctly scaled 1:76 body, so the bodies grew and the track stayed put.
Plenty of real railways were built narrower than standard gauge because it was cheaper through mountains. Modellers exploit this beautifully: take the track from a smaller scale and the models from a larger one, and you get a charming little railway that turns in half the space.
O scale models (1:48) on 16.5 mm HO track, representing 30 in gauge. Big, characterful locomotives that go round an 18 in radius. Hugely popular for that reason.
HO scale on 10.5 mm track = 3 ft gauge. Colorado narrow gauge, the Rio Grande, and some of the finest models ever made.
4 mm or HO models on 9 mm N-gauge track. Welsh slate quarries and continental feldbahnen in a space the size of a briefcase.
Garden-scale bodies on 16.5 mm track representing 15 in gauge industrial lines. Enormous models, tiny railway, tabletop space.
The letters give the scale, the number after the n gives the prototype gauge in
feet or inches: HOn3 is HO scale, 3 ft gauge. European practice uses letters
instead: e ≈ 750 mm, m ≈ 1,000 mm, so HOm is HO
scale metre gauge on 12 mm track.
Answer the first question that applies to you.
N. A 20-wagon freight is 1.5 m long and looks right on a 2 m × 1 m board. In HO the same train needs a garage.
HO or OO. Everything is made in it, including the obscure thing you will want in three years' time.
O, or On30. Coupling by hand is pleasant rather than fiddly, and the detail is visible without a lens.
G. It lives outside, it is nearly indestructible, and a battery-radio locomotive removes track wiring from your life entirely.
HO/OO switching, or 009. Small track plan, high detail, no continuous run needed.
That one. Sunk cost is a bad argument for buying, and a fine argument for starting.