HO vs N vs O model railroad scales: a practical size guide
Compare common model railroad ratios, convert dimensions between layouts, and understand why named scales can vary by region and standard.
How it works
Common working ratios include HO at about 1:87.1 in North America and much of Europe, N commonly at 1:160 in North America, and O often at 1:48 in the United States. Named scales are not globally identical, so verify the ratio used by your track, rolling stock, plans, and manufacturer.
Checked example
A 100 mm building made for N scale 1:160 becomes about 183.7 mm at HO 1:87.1. The same N-scale building becomes about 333.3 mm at O 1:48. These calculations resize linear dimensions; area, volume, material thickness, and mechanical fit change differently.
Workshop notes
Before resizing a structure or 3D file, confirm one known dimension and check clearances, track centres, couplers, wheel standards, and minimum printable features. A mathematically correct percentage does not guarantee compatibility with a particular railroad standard.
Compare ratios, not names alone
The denominator tells you the actual linear relationship. A lower denominator produces a larger model. O at 1:48 is therefore larger than HO at about 1:87.1, which is larger than N at 1:160.
Recognize regional differences
Named railroad scales can use different ratios and track gauges in different countries. Enter the published 1:N ratio for your specific project rather than relying on a label alone. Manufacturer documentation and recognized standards organizations are the best references.
Convert a structure between scales
For a 100 mm N-scale structure at 1:160 moving to HO at 1:87.1, multiply 100 by 160 and divide by 87.1. The result is about 183.7 mm. Enter all three building dimensions together so the proportions remain consistent.
Calculate a 3D slicer percentage
The same ratio produces a slicer setting: 160 ÷ 87.1 × 100 is about 183.7 percent. Going from HO to N gives about 54.44 percent. Verify the software uses uniform scaling on every axis.
Check compatibility separately
Track gauge, flange profiles, coupler heights, loading gauges, curve radii, and electrical standards are not solved by a simple scale conversion. Treat resized scenery and structures differently from operational rolling stock.
Keep a conversion record
Record the source ratio, target ratio, original measurements, exact results, and rounded workshop values. A worksheet provides a repeatable reference when several buildings or scenery parts must be resized together.
Frequently asked questions
Which is larger: HO or N scale?
HO is larger. A typical HO denominator is about 87.1, while common North American N scale is 160.
Is O scale always 1:48?
No. O scale ratios vary by region and practice. Use the ratio stated for your specific standard or product.
What percentage converts N scale to HO?
For 1:160 to 1:87.1, the linear scaling percentage is about 183.7 percent.
Can I resize rolling stock with the same formula?
The dimensions can be resized mathematically, but operational compatibility also depends on track, wheels, couplers, clearances, and manufacturing tolerances.