Scale Model Size Converter
Real size to model size at any scale and back — plus what a step to the next scale really costs in shelf space and material.
The size is in whatever unit you typed — a ratio has no units of its own. Bulk is the solid volume, so it is the right guide to resin, filler and postage, and a fair one for paint only where the model is a simple shape. Nothing is uploaded.
A scale is a length ratio, and almost nothing you care about is a length
The division is the easy part. What surprises people is everything downstream: shelf space is an area, so it follows the square of the ratio, and resin, filler, weight and postage are volumes, so they follow the cube. A half-scale model is not half the model — it is an eighth of the material.
| Scale | A 40 ft boxcar | Shelf footprint | Bulk vs HO |
|---|---|---|---|
| Z (1:220) | 2.18 in | 1.2 sq in | 0.06× |
| N (1:160) | 3.00 in | 2.3 sq in | 0.16× |
| HO (1:87) | 5.51 in | 7.6 sq in | 1.00× |
| S (1:64) | 7.50 in | 14.1 sq in | 2.52× |
| O (1:48) | 10.00 in | 25.0 sq in | 5.97× |
| G (1:22.5) | 21.33 in | 113.8 sq in | 58.01× |
The same boxcar is 3.9 times longer in G than in HO, and 58 times the bulk. That is the figure that decides whether a collection fits the room, and it is not the one on the box.
Every step up is modest in length and large in everything else
Across both the railroad scales and the kit scales, not one step from one scale to the next more than doubles the length — and not one of them fails to more than double the bulk. Those two facts are the same fact, because the cube of anything above 1.26 is more than twice it.
| Step | Length | Shelf area | Bulk |
|---|---|---|---|
| N → HO | 1.84× | 3.37× | 6.20× |
| HO → S | 1.36× | 1.85× | 2.52× |
| S → O | 1.33× | 1.78× | 2.37× |
| 1:72 → 1:48 | 1.50× | 2.25× | 3.38× |
| 1:48 → 1:35 | 1.37× | 1.88× | 2.58× |
| 1:144 → 1:72 | 2.00× | 4.00× | 8.00× |
"HO is about twice N" is a fair description of the length — it is 1.84 times. It is a poor description of the model, which is 6.2 times the bulk. And the 1:144 to 1:72 step is exactly 2× in length, which makes it the cleanest illustration in the table: twice the length, 4× the shelf, 8× the plastic.
How to use
- Enter the real-world size in any unit you like.
- Enter the scale as the number after the colon.
- Read the model size in the same unit.
- Set a second scale to see what the step costs in bulk.
Frequently asked questions
How do I convert a real size to a model size?
Divide by the number after the colon. At 1:87 a 40-foot boxcar is 480 inches over 87, which is about 5.5 inches. The arithmetic is the same whatever unit you started in, because a ratio has no units of its own.
Why does the tool not ask for units?
Because it does not need them. Feed it millimetres and you get millimetres; feed it feet and you get feet. The only place units matter is when you mix them, and the tool cannot see you doing that — so keep both figures in one unit.
Is 1:72 half of 1:35?
In length, roughly — 72 over 35 is about 2.06, so a 1:72 kit is a little under half as long. In everything else it is nowhere near half: it is about one ninth of the material, the weight and the shelf volume.
How much bigger is HO than N?
About 1.84 times in length, which is why people say "roughly twice". It is 6.2 times the bulk, which is the figure that decides whether a collection fits the room, and it is not the one on the box.
Why does a small step in scale cost so much space?
Because a scale is a LENGTH ratio while shelf space is an area and material is a volume. Area follows the square of the ratio and volume the cube, so a 1.5x step in length is 2.25x the shelf and 3.4x the resin.
Is a half-scale model half the model?
No — it is an eighth. Half the length, half the width and half the height multiply out to one eighth of the volume, so it takes an eighth of the filler, an eighth of the resin and weighs an eighth as much.
Does bulk predict paint too?
Only loosely. Paint covers a surface, so it follows the square rather than the cube, and only on a simple shape — a detailed model has far more surface than its outline suggests. Treat the area column as the better guide for paint.
Does this send anything anywhere?
No. Every figure is computed in your browser, and nothing is uploaded or stored.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.