Tiny Online Tools
The 20 mm cube that came in at 0.787
STL, OBJ and PLY files are lists of coordinates. None of the three records a unit anywhere in the file. A vertex at 20.0 might mean 20 millimetres, 20 centimetres, 20 inches or 20 metres — the number alone cannot tell you, so every program that opens the file has to assume something. Slicers assume millimetres. SketchUp exports inches. A CAD package set to metres writes 0.02 for a 20 mm cube.
That is why a 20 mm calibration cube turns up as 0.787 units: 20 ÷ 25.4. The fix is one multiplication — but only once you know which one.
What this tool does
It measures the bounding box, then works out what the model would measure under every plausible interpretation: millimetres, centimetres, inches, metres, and the two conversion mistakes that actually reach people — a ÷1000 export, and a millimetre model that was run through an inch conversion. Each candidate is ranked by how realistic the resulting size is for something a person prints, with a bonus when all three dimensions land on whole millimetres, because authored objects usually do and mis-scaled ones usually do not.
The whole ranking is shown with the resulting dimensions, not just one answer, and the reasoning is spelled out. It is an inference, not a reading. You decide.
When it is not a guess
3MF and STEP do declare their units, and those are read from the file rather than inferred. A 3MF's unit attribute is picked up directly; a STEP file's length unit comes from its header.
The things people get wrong
- Volume goes with the cube of the factor. Doubling a model does not double the resin — it multiplies it by eight. The before-and-after table spells the multiplier out.
- Per-axis scaling rescues a model that arrived squashed on one axis, which no uniform scale can.
- Baked, not transformed. The scale goes into the vertex positions themselves. STL has nowhere to keep a node transform, so anything left on one is simply lost on export.
Use it for
Rescuing SketchUp and Fusion exports, matching a replacement part to a measured dimension, resizing a model to fill a build plate, and checking a part against seventeen printers' build volumes before you slice it.
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