Scales & Gauges — The Irish Modeller's Guide

OO Scale — The Irish Default

OO (1:76 scale, 16.5mm track gauge) is the dominant scale in Irish model railways — as it is in Britain. The vast majority of Irish clubs, exhibition layouts, and commercial products are in OO. If you want the easiest path to a credible Irish layout, this is your scale.

The critical development in recent years has been the emergence of dedicated Irish-outline RTR manufacturers. Irish Railway Models (in partnership with Accurascale) now produces ready-to-run models of Irish locomotives and rolling stock to a standard that matches the best British OO products. Their releases include ex-CIÉ and Iarnród Éireann locomotive classes, coaching stock, and wagons. Clark Railworks handles pre-owned and collector-grade Irish OO stock. The range is small compared to the vast British catalogue, but it is growing every year.

British OO models from Hornby, Bachmann, Heljan, Hatton's, and others can also be used on Irish layouts — particularly for locomotive types that were shared between the British and Irish networks (ex-GWR locos, diesel shunters, some wagon types). Just watch the livery and lettering; a BR blue locomotive will look wrong on an Irish layout unless you're modelling a preserved line.

OO at Irish Broad Gauge (IBG) — 21mm

IBG is 1:76 scale (OO) with 21mm track — the accurate gauge for Irish mainline modelling. It's a minority practice in Ireland, but a committed minority: the MRSI has members who build IBG layouts of considerable quality, and the results are noticeably more convincing at close range than 16.5mm OO.

The challenges: commercial track in 21mm is scarce (you build your own or source from specialist suppliers). Most OO mechanisms need their wheelsets respaced to 21mm. Bachmann and Accurascale Irish models come with 16.5mm wheelsets; conversion kits exist but add cost. Pointwork must be built from scratch.

The reward: when you photograph an IBG Irish mainline layout, the proportions look right. The vehicles sit at the correct height relative to the rails. If you're committed to long-term accuracy and enjoy trackwork, IBG is worth considering from the start — retrofitting an existing 16.5mm OO layout is much harder than building IBG from scratch.

N Gauge — Small Space, Long Runs

N gauge (1:148, 9mm track) is Britain's second most popular scale, and the same applies in Ireland. Its main appeal is space: a 4×2ft baseboard in N gauge can represent the same length of prototype as a 6×4ft OO layout. This makes N gauge attractive for anyone with a small spare room or a corner of a bedroom.

The drawback for Irish modellers is a thin RTR selection. Graham Farish (Bachmann's N gauge brand) has produced some Irish-outline locomotives over the years, but the catalogue is limited. Most Irish N gauge modellers use British outline stock, or adapt continental models, and build their Irish scene through scenic modelling rather than prototypically-correct stock. It's a valid approach — Irish landscape and infrastructure (signals, crossing gates, station architecture) can make a layout clearly Irish even with generic rolling stock.

HO — The Global Standard (Not Recommended for Irish)

HO (1:87, 16.5mm) is the dominant scale in Europe, North America, and most of the world — but it's unusual in Britain and Ireland. The reason: Britain went OO in the 1930s for commercial reasons (fitting motors into small models), and the 1:76 standard stuck. Ireland, inheriting the British hobby market, followed OO.

HO shares the same 16.5mm track as OO but uses a slightly smaller ratio (1:87 vs 1:76). An HO locomotive next to an OO locomotive on the same track looks noticeably smaller. There is essentially no Irish-outline HO production. Unless you're modelling a continental or US prototype, or are already invested in HO from another country, there is no practical reason to choose HO for Irish modelling.

OO9 / 009 — The Irish Narrow Gauge Scale

OO9 (or 009) is the scale for modelling Ireland's extensive narrow gauge heritage. It combines OO's 1:76 ratio with N gauge's 9mm track — which accurately represents 3ft (914mm) gauge at 1:76 scale (true representation would be 11.9mm, giving a very small error that few find objectionable).

The County Donegal Railways, Cavan & Leitrim Railway, West Clare Railway, Tralee & Dingle, Cork, Blackrock & Passage, and many other 3ft gauge lines are all OO9 subjects. The scale has a dedicated community through the 009 Society, which produces a magazine, kits, and organises UK and Irish members.

Commercial OO9 mechanisms come from several manufacturers: Minitrains, older Egger-Bahn items (increasingly collectible), and Kato-based 009 Society specials. Bodies for Irish prototypes are almost entirely scratch-built or 3D-printed — but this is manageable for most modellers, since Irish narrow gauge locos tend to be small and geometrically simple.

O Gauge — High Detail, High Cost, High Space

O gauge (1:43.5, 32mm track) is the domain of the serious scratch-builder and high-detail collector. Locomotives at this scale are substantial objects — a 4-6-0 steam loco in O gauge is roughly 45cm long. Detail work is correspondingly rewarding; you can model rivet heads, cab fittings, and nameplate lettering with conviction.

Irish O gauge RTR production is essentially non-existent. This is scratch-build or kit-build territory. However, several Irish modellers have produced outstanding O gauge layouts of Irish prototypes — CIÉ, GNR(I), and narrow gauge subjects all lend themselves to O gauge's generous proportions. Space requirements are the main limiting factor: a meaningful O gauge layout needs at minimum a long garage or dedicated room.

Garden Railways — G Scale and SM32

Garden railways — typically 1:22.5 (G scale) or 1:32 (SM32), running on 45mm track — are a niche but committed part of the hobby in Ireland. The main appeal is weatherproofing: these models are built to live outdoors through Irish weather, running in a garden setting that can include real plants, paths, and miniature structures.

Irish-prototype garden railway stock doesn't exist commercially; anything Irish here is scratch-built or freelance. The fun is in the engineering and the garden, more than prototype accuracy. Irish weather — damp, mild, rarely freezing hard — is actually well-suited to garden railways: the main risk is flooding rather than frost heave.

Scale Comparison — Physical Size

To make the scale differences concrete, here's how a typical mainline diesel locomotive (say, a CIÉ 071-class, about 18.6m long in real life) appears in each scale:

These sizes explain why OO has become the dominant scale for home layouts: large enough to detail convincingly, small enough to fit in a reasonable room. N gauge's compactness allows longer runs and bigger scenes in the same space — a trade-off that suits many modellers.