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Randozi
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Model Train Scale Speed Calculator

Time your locomotive over a measured distance and see how fast it would be at full size, or enter a target speed and get the time it should take over your test track.

Scale speed

15.678 km/h

9.742 mph · the model covers 50 mm/s

The figure is only as good as the timing: time a steady stretch, away from acceleration, and repeat the run.

How it works

  1. Choose a scale from the list, or choose “Other” and type the ratio (87.1 for 1:87.1).
  2. Enter the measured distance in millimetres and the time in seconds (or use the timer).
  3. Read the scale speed in km/h and mph, and the speed of the model in mm/s.
  4. Or switch to “Target speed” to get the time to aim for over the same distance.

What people use it for

  • Checking a locomotive

    Does your loco really run at a believable scale speed at half throttle? Time it over 1 metre.

  • Matching two locomotives

    Time both over the same stretch to match their speeds in a consist.

  • Setting up a test track

    Find how long a run should take for 40 km/h, then adjust the controller until it does.

Questions

What is the formula?
Scale speed (km/h) = (distance in mm ÷ time in s) × n × 0.0036. The model's speed in mm/s times the ratio n is the full-size speed in mm/s, and 0.0036 converts mm/s to km/h. 100 mm in 5 s at 1:100 is 7.2 km/h.
And the time for a target speed?
Time (s) = distance × n × 0.0036 ÷ speed in km/h. 1,000 mm at 1:100 for 36 km/h takes 10 seconds.
Does it measure my locomotive's real top speed?
It converts the run you timed, so it is only as good as your measurement. Time a steady stretch, away from acceleration, and repeat the run a few times.
Does the timer replace a stopwatch?
It is a simple start and stop button that fills the time field. For lap times or several runs, use the stopwatch page.