Loading calculators...
Fetching calculator categories and tools for this section.
Preparing tools and content for you. This usually takes a second.
Fetching calculator categories and tools for this section.
Quick answer — HO scale length & prototype converter
At ratio 1:87 (HO — 1:87), a 40 ft prototype car scales to 5.5172 in (140.1379 mm) on the layout. A 50 ft car in N (1:160) → 3.75 in (95.25 mm). Reverse mode expands a measured model back to prototype feet. Linear length only—not track gauge.
Free HO scale calculator and N/O/G scale converter for benchwork, laser-cut structures, and consist planning. Browse the DIY & hobbies hub.
Last updated October 9, 2026
NMRA wheel and track standards differ from carbody length scaling. Use manufacturer turnout diagrams for geometry; this tool answers “how long in inches/mm?” along one axis.
Need a branded layout or club planning tool? Get a Quote
HO — 1:87 · Model size
0.140138 m
140.1379 mm · 5.5172 in · 0.45977 ft
Track gauge, wheel standards, and era-specific O scales differ by region. Use manufacturer drawings for turnout geometry; this tool is linear length only.
Tip:
For a 40 ft boxcar in HO (1:87), choose prototype → model, enter 40 ft, scale HO—output is the scaled length along the car body axis only (not track centerline offset).
Citation-friendly prototype ↔ model results from the live calculator engine.
| Scenario | Scale | Input | Inches | mm | Model ft |
|---|---|---|---|---|---|
| 40 ft boxcar in HO (default demo) | HO — 1:87 | 40 ft | 5.5172 | 140.1379 | 0.45977 |
| 50 ft car in N scale | N — 1:160 | 50 ft | 3.75 | 95.25 | 0.3125 |
| 40 ft car in O scale (US 1:48) | O (US) — 1:48 | 40 ft | 10 | 254 | 0.833333 |
| 40 ft car in G (1:22.5) | G — 1:22.5 (common) | 40 ft | 21.3333 | 541.8667 | 1.777778 |
| 5.52 in HO model → prototype length | HO — 1:87 | 5.5172 in | 479.9964 | 12191.9086 | 39.9997 |
| Scale | Ratio |
|---|---|
| Z — 1:220 | 1:220 |
| N — 1:160 | 1:160 |
| TT — 1:120 | 1:120 |
| HO — 1:87 | 1:87 |
| S — 1:64 | 1:64 |
| O (US) — 1:48 | 1:48 |
| O (UK / 7 mm) — 1:43.5 | 1:43.5 |
| G — 1:22.5 (common) | 1:22.5 |
UK O (7 mm/ft) and US O (1:48) differ; garden G may use 1:20.3 or 1:29—pick Custom 1:N when needed.
Ratios
1:220 … 1:22.5
Museums & narrow gauge
Flexible N
Input
One dimension at a time
Model → prototype
Ruler audits
Scope
Length along one axis
CNC & laser
Sub-mm output
40 ft prototype freight car in HO (1:87), prototype → model:
5.5172 in
≈ 140.1379 mm · true scale length along the body
Model railroading scales lengths by a fixed ratio between the real world and the layout. If the ratio is 1:N, every N units of prototype length equals one unit on the model. The calculator converts your input length to millimeters internally, divides or multiplies by N depending on direction, then shows millimeters, inches, feet, and meters so you can copy the number into CAD, a chop saw fence, or a caliper without hand-converting units. Worked example: 40 ft prototype in HO → 5.5172 in (140.1379 mm) because 40 ft = 12192 mm prototype, divided by 87.
model_length = prototype_length ÷ Nprototype_length = model_length × NLengths are converted to millimeters first so ft, in, m, cm, and mm inputs stay consistent.
Also explore our RC car gear ratio calculator for surface RC drivetrain math in another hobby aisle.
Get Custom Calculator for Your PlatformShare it with your modular group or scenery build night thread.
Suggested hashtags: #ModelRailroad #Trains #HOScale #NScale #Calculator