Learn: how STEP to STL works, question by question
This is the index of every explainer on the site. Each page was written from measurements taken on the machine that wrote it, and npm test re-runs those measurements before the page is published. A number that the tests cannot reproduce does not appear here.
- How to convert STEP to STL, in order — the six steps from the extension and the declared unit through the quality setting to the byte count you should get back.
- How to verify a STEP to STL conversion — five checks you can run with a file size, an edge count and a bounding box, with no CAD licence and no second tool.
- STEP vs STL — what the two formats actually store, why the output can be smaller or larger than the input, and why the reverse direction is a reconstruction rather than a conversion.
- A STEP file looks wrong — how to tell an ordinary faceted surface from a genuinely damaged file by judging the flat faces instead of the curved ones.
Which one to read first
| Nothing converted yet | Start with the workflow. Its first screen is the whole procedure, and steps 2 and 3 (unit, quality setting) are the two choices that change the output. |
|---|---|
| Converted, want proof | Go to verify a conversion. Check 1 alone tells you whether the file you were handed contains the triangles the converter claimed. |
| The preview looks faceted | Read a STEP file looks wrong. Faceting is normal; the page gives the number that separates “coarse setting” from “broken file”. |
| Choosing a format to keep | Read STEP vs STL. It is the page that explains why you should keep the STEP file and treat the STL as disposable. |
| Arguing with a number | Any of them. Every page ends with a section named Where these numbers come from that says how each figure was produced. |
The one formula worth memorising
For a binary STL the size is fixed by the triangle count: 84 bytes of header plus 50 bytes per triangle, so the file length tells you what is inside it. The flat 10 mm test cube converts to 12 triangles at every quality setting and lands as exactly 684 bytes. Curved geometry is where the count moves: the same cone measures 286 triangles at Draft and 2,142 at Fine. Recovering the count from the byte length is the first of the five checks on the verification page, and it is the reason you never have to trust a converter’s word for what it produced.
How these pages are written
- One page per question with a checkable answer. Questions that can only be answered by opinion, or that are really product advertising in disguise, do not get pages.
- Figures are measurements, not rules of thumb. Each page names its source at the bottom, and the test suite recomputes it rather than reading it back off the page.
- Pages get merged or retired when they overlap. When that happens the link is removed from this index and from the page footer on the same day, so nothing listed here is a dead end.
- What the tool itself accepts. STEP and IGES files —
.step,.stp,.iges,.igs— written out as STL, in millimetres by default, with your file never leaving the browser tab.
The converter is on the front page. Who runs it and what it will not do is on the about page; how your data is handled is in the privacy policy; a problem worth reporting is described on the contact page.