Editing HO scale (section)

{{Short description|Model railroad scale of 1:87}}
{{Use dmy dates|date=July 2020}}
{{Infobox model rail scale
| name = HO (H0)
| image_filename = HO Scale Bachmann 44-tonner.JPG
| image_caption = HO scale (1:87) model of a center cab [[switcher locomotive]] made by [[Bachmann Industries|Bachmann]], shown with a pencil for size comparison.
| scale = 3.5&nbsp;mm to {{cvt|1|ft|mm|0}}
| ratio = {{ubl|1:87 (world)|1:80 (Japan)}}
| standard = {{plainlist|
* [[Normen Europäischer Modellbahnen|NEM]] 010
* [[National Model Railroad Association|NMRA]] S-1.2
}}
| gauge = {{Track gauge|16.5mm}}
| prototype_gauge = [[Standard gauge]]
}}

'''HO''' or '''H0''' is a [[rail transport modelling scale]] using a 1:87 [[scale model|scale]] (3.5&nbsp;mm to 1&nbsp;foot). It is the most popular scale of [[Rail transport modelling|model railway]] in the world.<ref>{{cite web |url=http://mrr.trains.com/how-to/get-started/2011/11/your-guide-to-scales-and-gauges |title=Guide to model railroading scales and gauges |work=[[Model Railroader]] |date=2 November 2011 |access-date=2 October 2016 |archive-date=22 June 2015 |archive-url=https://web.archive.org/web/20150622045933/http://mrr.trains.com/how-to/get-started/2011/11/your-guide-to-scales-and-gauges |url-status=dead }}</ref><ref name=BasicModelRailroading>{{cite book |editor-first=Kent J. |editor-last=Johnson |title=Basic Model Railroading: Getting Started in the Hobby |url=https://books.google.com/books?id=4633V-K0ZQcC&pg=PA6 |year=1998 |publisher=Kalmbach Publishing, Co. |isbn=978-0-89024-334-3 |page=6 |access-date=2017-10-24}}</ref> The rails are spaced {{convert|16.5|mm|in|3}} apart for modelling {{Track gauge|1435mm}} [[standard gauge]] tracks and trains in HO.<ref name="Modeling Scales: Scale and Gauge">{{cite web |url-status=dead |website=[[NMRA]] |url=http://www.nmra.org/beginner/scale.html |title=Modeling Scales: Scale and Gauge |date=December 26, 2000 |access-date=4 March 2010 |archive-date=Mar 15, 2010 |archive-url=https://web.archive.org/web/20100315025519/http://www.nmra.org/beginner/scale.html }}</ref>

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 gauge|1]], [[2 gauge|2]] and [[3 gauge]]s introduced by [[Märklin]] around 1900. Rather than referring to the scale as "half-zero" or "H-zero", English-speakers have consistently {{Citation needed|date=April 2025}} pronounced it {{IPAc-en|eɪ|tʃ|_|oʊ}} 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 {{IPA|de|ha: 'nʊl|}}. In Japan, many models are produced using 1:80 scale proportions (16.5mm track is still used).