Practical tools for measured work
Model Train Scale Speed Calculator
Convert a timed run over a measured distance into scale mph and km/h, or find the time for a target speed.
Calculate the layout, check the diagram, then print the result for the shop or jobsite.
Length of a marked stretch of straight track.
Time the front of the locomotive between the two marks.
Optional. Enter 0 to skip.
Time the run over at least a few feet of straight, level track and average several runs.
How it works
Formula: scale speed is the distance the model covers, multiplied by the scale ratio, divided by the time. In HO (1:87.1), 1 inch per second is about 5 scale miles per hour. Metres per second convert to km/h by multiplying by 3.6 and to mph by dividing by 0.44704.
Timing a run: mark two points on straight, level track, run the locomotive at a steady throttle setting, and time it between the marks. Repeat in both directions and average the results.
Target speed: enter the scale speed you want to see, such as a prototype speed limit, and the tool shows how long the model should take to cover the marked distance.
Current-input example
The result above uses these exact values. This snapshot is included when the page is printed so the output can be checked against the original measurements.
- Measurement unit
- Inches
- Scale
- HO (1:87.1)
- Measured distance
- 36
- Time to cover it
- 8 s
- Target scale speed
- 40 mph
Primary result: Scale speed: 22.3 mph.
Before using the result
- Measure from the datum or reference edge described by this tool, and do not mix inside, outside and centerline dimensions.
- Keep inputs in the displayed units and preserve more precision than the final cutting or purchasing tolerance requires.
- When the result is close to a limit, verify it with a test piece, field measurement, manufacturer drawing or qualified project professional.
Limitations
Scale ratios follow common practice, and N scale is 1:160 in North America and 1:148 in the UK, so choose the one you actually model. Model locomotive speed changes with load, grade and voltage, so the result describes the tested run only. Locomotive speed also depends on the decoder speed table and throttle setting.
Frequently asked questions
Which scale ratio should I use for HO?
The NMRA uses 1:87.1 for HO. Many people round it to 1:87. British OO is 1:76.2.
How far should I time?
Use a straight, level stretch of at least a few feet, and time from the front of the locomotive to the same point at the far mark. A longer distance reduces timing error.
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