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STL to IGES converter.
To convert an STL mesh to IGES, drop the .stl file below, binary or ASCII, and download the .igs file it makes, free and with no account. The result is the faces of a faceted solid of flat faces, not the curved surfaces the mesh came from. It is built in your browser, so the file never leaves your computer unless you choose to send it to us, and it is checked against the mesh before you can download it.
Your file never leaves your computer unless you choose to send it to us: the conversion runs in your browser.
How to convert STL to IGES
- Drop the mesh. Drop your .stl file on the box above, or choose it from your computer. The page says at once whether it closes into a solid.
- Check the format. Convert to is already set to IGES (.igs).
- Press Convert. Small meshes take a few seconds. Above 10,000 triangles the page says how long it can take.
- Download the IGES. The line above the Download button says how many flat faces it made. Rename the file to .iges if your software wants that.
| STL to IGES | What happens |
|---|---|
| Reads | STL meshes (.stl), binary or ASCII, up to 250,000 triangles. Numbers are taken as millimetres. |
| Writes | IGES 5.3 (.igs): the flat faces of a faceted solid when the mesh closes, surfaces only when it does not. |
| Keeps | The mesh, exactly. In a closed mesh, triangles that lie exactly in one plane become one flat face. |
| Cannot recover | The curved surfaces the mesh came from. No IGES made from a mesh has a true cylinder in it. |
| Checks | Every face, plus volume and surface area to one part in a billion, against the mesh. |
| Costs | Free, with no account and no limit on how many files you convert. |
Think about STEP first
Most software that reads IGES today also reads STEP, and a STEP keeps a closed mesh as one solid instead of leaving the reader to join its faces. Our closed 2,338-triangle bracket also came out smaller that way: a 1.69 MB STEP against a 3.27 MB IGES. So if you have the choice, use STL to STEP. This page is for the cases with no choice, such as an older CAM package or a controller that takes IGES and nothing else, or a customer whose specification says IGES.
What arrives at the other end
Each flat patch of the mesh is written as one trimmed surface. A CAD or CAM program opening the file sees a part made of many small flat faces, often thousands, and it has to join them itself, so some programs will show loose surfaces until you run their knit or sew command. Toolpaths cut from it will follow the facets, because the facets are all there is. It is fine for fitting, measuring and simple flat work, and a poor basis for machining a curved surface.
Open meshes, touching bodies, big meshes
- Gaps. A mesh with a gap comes out as surfaces only, and the page calls it an open mesh. So does a closed mesh with one loose face anywhere in the file. Nothing is patched shut. In a batch the row says only Verified, so drop a mesh alone if that matters.
- Touching bodies. Closed bodies that touch or cross one another are not made into IGES at all, because where they meet, which side is solid cannot be told. The page says so as soon as the file is dropped.
- Big meshes. The converter refuses more than 250,000 triangles, it can use at most 4 GB of memory in a browser, and the page says how long it can take above 10,000. On a desktop PC 120,000 triangles took a little over three minutes to IGES and 1.4 GB.
How the IGES is checked
The IGES is read back and must have every face the triangles were made into, with the same volume and surface area as the mesh to one part in a billion. That is the converter's own reading of it. Another program may sew the faces at a tighter tolerance and leave them apart.
A measured example
We exported a 120 x 80 x 30 mm bracket modelled in SOLIDWORKS 2024 (a plate with a filleted, chamfered boss and five holes) as a 114 KB STL of 2,338 triangles. On a desktop PC it became a 3.27 MB .igs in 2.7 seconds, about 29 times the size of the mesh, and the check line read: "Verified: the IGES file was read back. It is a faceted solid, 1,631 flat faces made of the mesh's 2,338 triangles (triangles that lie exactly in one plane make one face), and agrees with the mesh on volume to 0.0001%, surface area to 0.0001% and size to 0.001 mm." Measured on 5 November 2026.
Credits and licences for the projects the converter is built on are on the converter page.
Questions
Can STL be converted to IGES with real curved surfaces?
No. The curved surfaces were lost when the STL was made, and this converter does not fit new ones by estimate. A round face comes out as a band of flat ones.
Why is the IGES so much bigger than the STL?
An STL lists triangles and little else. IGES gives every flat face its own surface and trim curves, in fixed-format text. Our 114 KB mesh became a 3.27 MB file.
Will my CAM software cut from it?
It should open, but it may arrive as loose surfaces until you run a knit or sew command, and toolpaths will follow the facets. For a clean cut, go back to the original CAD if anyone still has it.
Does it read ASCII STL files?
Yes, ASCII and binary alike. The numbers are taken as millimetres, and the IGES is written in millimetres.
Every conversion
| From | To STEP | To IGES | To STL |
|---|---|---|---|
| SLDPRT | SLDPRT to STEP | SLDPRT to IGES | SLDPRT to STL |
| X_T | X_T to STEP | X_T to IGES | X_T to STL |
| X_B | X_B to STEP | X_B to IGES | X_B to STL |
| STEP (.stp) | Already STEP | STEP to IGES | STEP to STL |
| IGES (.igs) | IGES to STEP | Already IGES | IGES to STL |
| STL | STL to STEP | STL to IGES | Already STL |
Quoting laser-cut parts from files like these?
Lasertally is Windows software for fabrication shops. It opens STEP, IGES, DXF and NC1 files, measures the pierces, cut length and bends off the geometry, and prices the part on your own rate card.