1:87.1
The precise HO scale ratio
One unit on the model represents 87.1 of the same units on the prototype. That makes HO a practical scale for detailed structures, vehicles, scenery, and rail operations.
Source and method ↓Reference library
HO Scale Model Railroad Statistics and Dimensions
Use this quick reference to turn prototype measurements into practical HO scale planning numbers. Every measurement is based on the National Model Railroad Association’s 1:87.1 HO scale reference.
Quick HO scale conversion table
| Prototype measurement | HO scale measurement | Useful for |
|---|---|---|
| 1 foot | 0.138 in. | Small trim and details |
| 10 feet | 1.38 in. | Doors, alleys, sidewalks |
| 20 feet | 2.76 in. | Small storefronts and lots |
| 40 feet | 5.51 in. | Building widths and railcars |
| 50 feet | 6.89 in. | Commercial facades and railcars |
| 100 feet | 13.78 in. | Long industrial fronts and larger structures |
0.138"
One prototype foot in HO scale
A one-foot prototype dimension becomes just under 9/64 inch on an HO model. This is the base conversion behind the reference measurements below.
Source and method ↓1.38"
Ten prototype feet in HO scale
Useful for estimating storefront widths, narrow alleys, loading doors, and sidewalk sections before cutting material.
Source and method ↓5.51"
Forty prototype feet in HO scale
A common building, freight car, or lot dimension becomes a little over five and a half inches on the layout.
Source and method ↓6.89"
Fifty prototype feet in HO scale
This is a helpful benchmark for larger storefronts, commercial facades, and a 50-foot railcar.
Source and method ↓13.78"
One hundred prototype feet in HO scale
At HO scale, a full city-block-sized building or long industrial frontage takes a little under 14 inches.
Source and method ↓0.651" / 16.5 mm
HO standard-gauge track target
The NMRA’s June 28, 2026 HO standard lists a 0.651-inch, or 16.5 mm, target track gauge, measured between the inside railheads.
Source and method ↓0.048" / 1.2 mm
HO standard flangeway target
For standard HO trackwork, the NMRA’s target flangeway is 0.048 inch, or 1.2 mm. It is a useful reference when checking turnout and guard-rail clearances.
Source and method ↓0.110"
Code 110 wheel width
The current NMRA HO standard identifies Code 110 as a 0.110-inch wheel width. This is a practical reference when matching wheels and trackwork.
Source and method ↓How to use the numbers
Divide prototype inches by 87.1.
For the values on this page, a prototype dimension in inches is divided by 87.1. For example, 40 prototype feet equals 480 inches. Dividing 480 by 87.1 gives 5.51 inches in HO scale. Values are rounded to two decimal places where shown.
Use the result as a planning guide, then account for the visual room you need for walls, sidewalks, roadways, and the details that make a scene feel lived in.
Explore HO scale craftsman kits →Methodology and sources
Built on published model railroad standards.
Primary source
The National Model Railroad Association’s current standard identifies HO as 1:87.1. Its June 28, 2026 track standard lists the HO standard-gauge target, flangeway target, and Code 110 wheel width used in the refreshed reference figures.
NMRA S-1.2 Standard Scales, May 16, 2026 ↗NMRA S-3.2 Trackwork, Standard Scales, June 28, 2026 ↗
Calculation method
Conversion values use the published 1:87.1 ratio. The conversion table was recalculated and the trackwork figures were checked against the NMRA standards on October 9, 2026. Measurements are not product specifications and should be checked against the instructions for the kit or component being used.
NMRA standards and recommended practices index ↗Cite this page
Red Arrow Lines, “HO Scale Model Railroad Statistics and Dimensions,” CraftsmanKits.com, updated October 9, 2026. Link directly to the statistic you are citing by using its heading.