Parametric models · practical guides
Check an STL before resizing it
An STL does not carry dependable unit metadata. Overall bounds are useful checks, but they do not automatically recover exact feature dimensions.
Choose and verify intended units
Import using the units you believe the source used, then compare displayed bounds with a known physical measurement. If the result is ten times wrong, revisit the unit assumption before editing geometry.
Do not overread mesh measurements
Bounds can verify overall size. Exact hole centers, bores, and curved features in a mesh may require manual inspection or a separate reconstruction workflow; this page does not promise automatic feature extraction.
The same STL numbers under three unit choices
The sample stores coordinates for a 30 × 20 × 4 mm plate. Interpreting those same numbers as centimetres makes the reported dimensions ten times larger; interpreting them as inches multiplies them by 25.4. These are actual local file-check worker results. Choose the source unit from a known measurement before resizing the geometry.
| Chosen source unit | Bounds, mm |
|---|---|
| mm | 30 × 20 × 4 |
| cm | 300 × 200 × 40 |
| in | 762 × 508 × 101.6 |
Questions this page answers
Why does my STL open ten times too large?
STL files do not reliably state their units. Reimport with the intended unit and compare displayed bounds with a known measurement before scaling.
How can I see an STL's dimensions in millimetres?
Choose millimetres for the inspection/import context and compare the reported overall bounds with a known dimension. Treat that as a bounds check, not complete feature metrology.
How do I check the distance between two holes in a mesh?
Use a mesh-capable measurement or reconstruct reference geometry manually, and verify against a known part when accuracy matters. PurCad does not claim automatic exact hole-center extraction.
Does resizing an STL also resize every hole?
Whole-mesh scaling changes every coordinate, including holes and wall thicknesses. Use editable source geometry for a controlled feature change.