HO scale
model railroad scale of 1:87 (3.5 mm:1 ft)
HO or H0 is a rail transport modelling scale using a 1:87 scale (3.5 mm to 1 foot). It is the most popular scale of model railway in the world. The rails are spaced 16.5 millimetres (0.650 in) apart for modelling 1,435 mm (4 ft 8+1⁄2 in) standard-gauge tracks and trains in HO.
The name HO comes from 1:87 scale being half that of O scale, which was originally the smallest of the series of older and larger 0, 1, 2 and 3 gauges introduced by Märklin around 1900. Rather than referring to the scale as "half-zero" or "H-zero", English-speakers have consistently pronounced it and have generally written it with the letters HO. In other languages it also remains written with the letter H and number 0 (zero); in German it is thus pronounced as [ha: 'nʊl]. In Japan, many models are produced using 1:80 scale (16.5 mm track is still used).
History
After the First World War there were several attempts to introduce a model railway about half the size of 0 scale that would be more suitable for smaller home layouts and cheaper to manufacture. H0 was created to meet these aims. For this new scale, a track width of 16.5 mm (0.65 in) was designed to represent prototypical standard-gauge track of 1,435 mm (4 ft 8.5 in) width, and a model scale of 1:87 was chosen. By as early as 1922 the firm Bing in Nuremberg, Germany, had been marketing a "tabletop railway" for several years. This came on a raised, quasi-ballasted track with a gauge of 16.5 mm, which was described at that time either as 00 or H0.
Begin with the source’s own compact description: “HO scale” is model railroad scale of 1:87 (3.5 mm:1 ft). The dossier treats that line as a proposition to test through scale, model and railroad, not as a finished interpretation.
Why this record matters
The phrase “model railroad scale of 1:87 (3.5 mm:1 ft)” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated May 19, 2026. The linked authority identifier is Q911411. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1900 and 1922.
The absence of detail may reflect summary conventions rather than a lack of surviving documentation. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “HO scale”, its source revision and the description used here.
- Expand the search: follow HO scale primary sources, HO scale archive and scale research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “HO scale”?
- Which institution is responsible for the underlying evidence?
- Which cited source is closest to the event, object or claim?
Search terms from this dossier
This entry incorporates text from “HO scale” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.