🚄 Scale Speed Calculator

Enter your model train's actual speed (measured in inches per second, e.g. with a stopwatch and a measured track section) and your scale to calculate the equivalent real-world speed in scale mph — helpful for running trains at realistic-looking speeds.

Model speed (in/sec)

Scale

From inches per second to scale mph

The model's speed is multiplied by the scale ratio to get prototype inches per second, then converted to miles per hour - 3,600 seconds in an hour, 63,360 inches in a mile:

scale mph = model in/sec x ratio x 3600 / 63360
          = model in/sec x ratio x 0.056818

10 in/sec in HO = 10 x 87.1 x 0.056818 = 49.5 mph

That collapses into a handy constant per scale: one inch per second is 4.95 scale mph in HO, 9.09 in N, 2.73 in O and 12.5 in Z. Multiply your measured in/sec by the figure for your scale and you have the answer without the tool.

Measuring the model speed accurately

The input is the number most people get wrong. Mark a measured section, run the train at a fixed throttle setting and time it end to end:

model in/sec = section length in inches / seconds taken

30 in section timed at 3.0 sec = 10 in/sec

Use a long section. Half a second of stopwatch reaction over a 3-second run is a 17 per cent error; over a 12-second run it is 4.
Time it both ways and average. Grade and track condition change the speed noticeably in one direction.
Note the throttle step. The point of the exercise is a chart of speed against notch, so you can find 25 mph again next session.

Scale speed shrinks distance, not time, and a model always looks faster than the number says because you are watching from what would be half a mile away. Realistic running usually means slower than feels right.

Frequently asked questions

How fast is 10 inches per second in HO scale?

49.5 scale mph - respectable freight speed. The same 10 inches per second is 90.9 mph in N and 27.3 mph in O.

How fast should a switching move be?

Under 10 scale mph, which in HO is about 2 inches per second. It feels far too slow on a small layout and is exactly right.

How do I measure my train's speed?

Time it over a marked stretch of straight track and divide the length in inches by the seconds. Keep the throttle steady, use as long a run as you have, and average two passes.