I'm a little late to the party here, but that won't stop me from throwing in my 2¢.
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If Traveller assumes 1.5 m squares represented by a 15mm grid then 1:100 is a good fit, but when it comes to scales there is a little sillyness.
The real sticking point is that most miniatures assume assume a 6' (or so) man, while most games assume a 5' (or so) game grid. Even Traveller, which uses 1.5 meter {59 in, or 4.91 feet} squares. So the 15mm tall miniature man is at closer to 1:120, while the game grid is at 1:100.
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Fortunately we live in the modern age of 3D printing and STL files, so you can scale your terrain and miniatures as suits you. For 1:100 or a 1.5m game grid at 15mm or .59" you can snag any number of miniatures and terrain and scale them to fit. A 6' man would be 18.28 mm tall at this height. 3D slicing software lets you scale STL files either by percent, or to a specific dimension. So if you grab some shipping container files from somewhere you can scale them to be ~60 mm or 120mm long depending on if it's a 20 or 40 foot container.
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The real issue is that real world, interalmodal shipping containers don't conform exactly to Traveller's 1.5m x 1.5m x 3.0m standard grid. the length is good, 6.058m or 12.192m the width is odd at 2.438m and the standard height is either off, at 2.59m or close at 2.89m. Out of the 3 dimensions width is the real problem child. Stretching a standard 20' container file 20% in width and 10% in height gives a 2.9m x 2.9m X 6m cube, which fits nicely with Traveller's grid, and gives a nice 4 dTon unit of cargo.
The 15mm miniature would be a 5ft man, and the 18mm miniature would be a 5'10 man.
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