🚂 Scale Conversion Calculator

Enter a real-world dimension and pick a model railroad scale to convert it to the equivalent model size, or switch direction to convert a model measurement back to real-world size.

Divide going down, multiply coming back

The ratio is the only number in the sum. Everything is in inches, so a prototype dimension in feet must be multiplied by 12 first:

model = real size / ratio
real  = model size x ratio

40 ft boxcar = 480 in  ->  480 / 87.1 = 5.511 in in HO
50 ft car    = 600 in  ->  600 / 160  = 3.750 in in N
a 6 ft brakeman = 72 in ->  72 / 87.1 = 0.827 in in HO

Results appear to three decimals of an inch and again in feet, the row to read when Model to Real-world returns a large answer. Check the direction selector first: a figure left in the box converts the wrong way round without complaint.

The ratios, and why they are not tidy

Model scales grew out of "so many millimetres to the foot", which is why they land on awkward numbers. HO is 3.5 mm to the foot - 304.8 divided by 3.5 is 87.1, not 87. N is a flat 1:160 in North America and continental Europe, but British N is 1:148 and Japanese N is 1:150 on the same 9 mm track. O is the least settled of all: 1:48 in the United States, 1:45 in much of Europe and 1:43.5 in Britain, all running on 1.25 inch track.

Scale is the ratio; gauge is the width between the rails. G is a gauge, not a scale - 45 mm track carries models from 1:32 to 1:20.3, and 1:22.5 is only the most common. Narrow gauge codes such as HOn3 keep the scale and narrow the track.

Frequently asked questions

How long is a 40 foot boxcar in HO scale?

5.511 inches over the body: 480 inches divided by 87.1. Couplers add a little to the length over pulling faces.

What is the difference between scale and gauge?

Scale is how many times smaller the model is than the real thing. Gauge is the distance between the rails - 16.5 mm for HO, 9 mm for N. Two models in different scales can share a gauge.

Why is HO 1:87.1 rather than 1:87?

Because it was defined as 3.5 mm to the prototype foot, and 304.8 mm divided by 3.5 gives 87.086 - rounded to 87.1 in the standards.