Converting between scales for kitbashing
You have plans at 1:48 and want to build at 1:72, or a box of 1:72 parts to use on a 1:76 layout. The arithmetic is one line. Deciding whether the mismatch will show takes judgement.
The formula
new size = old size × Nold ÷ Nnew. This keeps the real object the same and changes only the model. For example:
- An 80 mm part at 1:72, redrawn at 1:48: 80 × 72 ÷ 48 = 120 mm.
- A 250 mm hull at 1:35, wanted at 1:72: 250 × 35 ÷ 72 = 121.5 mm.
- To rescale a 3D-print file or a scan of plans, use the factor Nold ÷ Nnew as a percentage. 1:48 → 1:72 is 66.67%, and 1:72 → 1:48 is 150%.
The converter's Scale → scale mode does this for length, width and height together and shows the area and volume factors.
How close is "close enough"?
There's no standard tolerance. It depends on what the part sits next to. Here are the size differences between some scales that often get mixed:
| Pair | Size difference | On a 1.8 m figure |
|---|---|---|
| 1:72 vs 1:76.2 (OO) | 5.8% | 25.0 vs 23.6 mm |
| 1:76.2 vs 1:87 (HO) | 14.2% | 23.6 vs 20.7 mm |
| 1:43.5 vs 1:48 | 10.3% | 41.4 vs 37.5 mm |
| 1:32 vs 1:35 | 9.4% | 56.3 vs 51.4 mm |
| 1:48 vs 1:72 | 50% | 37.5 vs 25.0 mm |
Percentages are Nlarger ÷ Nsmaller − 1. Natural objects such as rocks, trees and crates come in so many real sizes that a 10–15% mismatch rarely shows. Things with a standard real size, like doors, steps, wheels, rails and people, give a mismatch away much sooner, especially side by side. When in doubt, put the two parts together and look from normal viewing distance.
Watch out for
- Thickness. Panel lines, sheet thickness and moulded detail often aren't to scale in kits, because plastic has minimum practical thicknesses. A part scaled down from 1:35 to 1:72 can end up too thin to print or mould.
- Printer minimums. Resin and filament printers have a smallest reliable feature size. Check your printer's documentation before shrinking details.
- Material and weight. Volume changes with the cube of the factor. Scaling a print up 150% uses about 3.4 times the material.
Use the scale comparison to see the differences visually, and keep conversions for a build together in a project.