Model Scale Calculator

Modellers deal with three ways of saying the same thing. A ratio like 1:76 is the honest one. A figure height like “28mm” is a ratio in disguise, and which ratio depends on whether the 28mm is to the eyes or the top of the head — which is exactly why two ranges both called 28mm do not match on the table. An architect's 1:50 is the same arithmetic used the other way round.

Start from a named scale

Scale ratio, as the number after 1:

76.2 for OO, 87 for HO, 50 for an architect's drawing.

A real measurement in millimetres

Scaled down to the model.

A model measurement in millimetres

Scaled up to real life.

Figure height in millimetres

The number a range is sold as, like 28mm.

Measured to

How tall a real person is, in millimetres

1750 is a common assumption.

4500mm becomes 59.06mm at 1:76.2

Going the other way, 60mm of model is 4.57m in real life. One metre is 13.12mm at this scale.

A 28mm figure measured to the eyes represents about 1:59 — nearest named scale 1:50 at 1:50.

✓ Scaling down and back up returns the measurement — 4500mm at 1:76.2 is 59.06mm, which scales back to 4500mm
✓ Scaling up and back down returns the model measurement — 60mm of model is 4.57m in real life
✓ The figure height gives back the ratio it implies — 28mm measured to the eyes for a 1750mm person is 1:59
✓ A metre becomes what the ratio says — one metre is 13.12mm at 1:76.2
✓ The nearest named scale is the nearest one — 1:50 at 1:50, against the 1:59 the figure implies

What this generator does

Divides real measurements by the ratio and multiplies model ones back up, and turns a figure height into the ratio it implies given where the height is measured to.

How to use this tool

Pick a named scale, or type the ratio yourself.
Put a real measurement in to see what it becomes on the model.
Put a model measurement in to see what it represents.
For figures, set the height and where it is measured to.

Understanding the controls

Start from a named scale: Model railway gauges, common kit scales, architectural scales and map scales, all as plain ratios. Choosing one fills in the ratio below.
Scale ratio: The number after the colon. Everything on the page is this one number applied in one direction or the other.
A real measurement: In millimetres, taken from the thing itself. Dividing by the ratio gives the size to build. This is the direction that shows you what will not survive the shrink: at 1:76 a 3 mm handrail becomes four hundredths of a millimetre, which is nothing.
A model measurement: In millimetres, taken off the model with a rule or callipers. Multiplying by the ratio gives what it stands for full size, which is how you check a kit part against a drawing, or work out whether a doorway on the layout would let a person through.
Figure height: The number a range is sold as. On its own it is not a scale, because it says nothing about where the height was measured to.
Measured to: To the eyes, the top of the head, or including hair and headgear. The same 28mm is a noticeably different scale under each, which is why ranges that both say 28mm can look wrong together.
How tall a real person is: The height the figure is standing in for. 1750mm is the usual assumption, but a range built around taller heroic figures uses more.

Common use cases

Scaling a real building down for a model railway layout
Working out what a 28mm range really is in ratio terms
Checking whether two figure ranges will mix on the same base
Reading a measurement off an architect's drawing
Converting a kit's dimensions between 1:35 and 1:48

How this generator works

One number does all of it: dividing by the ratio scales down, multiplying scales up, and the check runs both directions and requires the measurement to come back to itself. The figure height is turned into a ratio by dividing the real person's height by the figure's full height — which is the quoted height adjusted for where it was measured to, since a figure quoted to the eyes is taller overall than the same number quoted to the head. That ratio is then compared against every named scale to find the genuinely nearest, which the check confirms by testing all of them.

Randomness and fairness

Nothing is random. The same ratio always converts the same way.

For how randomness is produced across the whole site, see how Generate Random works.

Limitations and good to know

Figure ranges are inconsistent in practice; two ranges at the same nominal scale can still differ in build and bulk.
OO gauge is a compromise — 1:76 bodies on 1:87 track — so it does not scale cleanly in both directions.
Heroic proportions make figures wider as well as taller, which no ratio captures.
Map scales are included for completeness, but a map's scale bar beats any arithmetic.

Privacy and your data

The conversions run in your browser. No measurements are transmitted or stored.