STL coordinates need an interpretation
Most STL files do not provide a reliable length-unit declaration. A coordinate value of 20 may mean millimeters or inches. Choose the unit used by the source application; this tool normalizes the output to millimeters and reports the resulting bounding dimensions.
Compare independent observations
Record the source bounding box before conversion. Open the exported STEP in the receiving application, check the three overall dimensions, then inspect a known edge or hole. A successful download alone does not demonstrate that the receiver interpreted the file as intended.
Keep the handoff reproducible
Save the STEP, source STL and report together. Record the exporting application and selected units. For very dense meshes, simplify a copy with a documented error tolerance before conversion: a huge faceted solid can be impractical even when the file is valid.
Work through a scale comparison
For a unit cube whose coordinates run from 0 to 1, selecting millimeters produces a 1 mm edge. Selecting inches produces a 25.4 mm edge because one inch is exactly 25.4 millimeters. Area changes by the square of that factor and volume by its cube. A wrong unit choice therefore affects more than the displayed width.
If an uploaded bracket should be 80 mm wide but the report says 2,032 mm, check whether inch interpretation was selected for millimeter coordinates. Correct the input choice and generate a new result; do not compensate by applying an unexplained scale factor later in a different application.
Verify the receiving file rather than its name
Open the downloaded STEP as a new document, inspect the body tree and measure all three overall dimensions. A file named with a STEP extension is not sufficient evidence by itself. The included normalized STL uses the same millimeter geometry as the STEP, making side-by-side overlays useful. Keep the source file separately because this normalized copy does not preserve the original byte representation or unit convention.