Convert IGS (IGES) to STL for 3D Printing
The surfaces in your .igs or .iges file are tessellated into a binary STL in millimeters, so it lands at the right size in a slicer. Because IGES faces are stored as separate patches and are not stitched during import, the mesh can contain cracks and is not guaranteed watertight, so plan on a repair pass.
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Turning IGES surfaces into a printable mesh
IGS and IGES are the same thing: the Initial Graphics Exchange Specification, with the short extension used by CAD programs that stuck with three-letter names. It stores a part as exact mathematical geometry, mostly NURBS surfaces and trimmed surface patches, which is useful for sending shapes between CAD systems and useless for a 3D printer. A slicer wants triangles, and it wants them in millimeters, so something has to tessellate the surfaces first. That is the whole job of this page.
The conversion runs on our servers with FreeCAD 1.1 and its OpenCASCADE 7.9 kernel. The file is read with Part.Shape.read, with a few repairs attempted first: a gzip-compressed export is unpacked, a UTF-16 file is re-encoded and a byte order mark is stripped. The resulting shape is then triangulated with MeshPart.meshFromShape using an absolute chord tolerance of 0.1 mm and a maximum facet angle of 0.5 radians, roughly 29 degrees. Those values are fixed for every file and every part size; there is no quality slider. The result is written as a binary STL containing every body from the file in one object, with no color and no names, since STL has nowhere to put them.
Two things to know before printing. Scale is handled: IGES geometry is brought in as millimeters, so the STL measures what the part measures and no rescaling is needed. Topology is not healed: IGES faces are not sewn during import, so patches meet only as closely as the original export placed them, and a verified IGES test part produced a mesh that was not watertight. Curved faces also become flat facets, and small features such as fillets and little holes get relatively few facets because of the angular limit. If the originating CAD system can export STEP or STL instead, either will usually give a cleaner starting point.
Most people arriving here were sent an .igs file by a client, a supplier or an old project archive and need something a slicer, mesh editor or CAM package will open. The same IGES upload can also be sent to OBJ, PLY, 3MF, OFF or STEP from the related pages, which is worth remembering if the mesh turns out to be for display rather than printing.
How to convert an IGS file to STL
- Export the IGES file with surfaces or solids included. A wireframe or curves-only export has no faces to triangulate and will be rejected as containing no valid 3D geometry.
- Keep the geometry in the file itself. IGES exports that only reference external part files carry nothing to mesh.
- Upload the .igs or .iges file here. Compressed exports are unpacked automatically, so there is no need to decompress first.
- Convert and download the binary STL. Most files finish in a few seconds; models with very dense surface sets take longer, and each job has a ten-minute engine limit. The download link lasts about four hours.
- Open the STL in your slicer and confirm the dimensions, which should already be in millimeters.
- Run the slicer's or mesh tool's repair function to close any gaps between patches before slicing, and check thin walls and small holes for missing facets.
What this converter does
- Triangulates IGES NURBS surfaces and trimmed patches with FreeCAD 1.1 and the OpenCASCADE 7.9 kernel.
- Writes a binary STL in millimeters, matching the default unit of every common slicer.
- Keeps all bodies from the file in one STL as separate shells, and writes stacked duplicate sub-shapes only once instead of doubling them.
- Repairs common transport damage before reading: a gzip-compressed export is unpacked, a UTF-16 file is re-encoded and a byte order mark is stripped.
- Accepts both .igs and .iges, and refuses uploads that are really a ZIP, PDF or native SolidWorks or Inventor file instead of producing an empty mesh (the on-screen wording is a generic "could not read this 3D file").
- No CAD install needed on either side: 50 MB per file as a guest, 100 MB with a free account, 200 MB on Plus, 1 GB on Pro, 10 files per batch (25 Plus, 50 Pro).
Video Tutorial
Detailed guide on how to convert IGS files to STL quickly, for free, and without losing original quality. Perfect if you need to process file formats, reduce size, or upload files to systems that only
Questions about IGS to STL
Is there any difference between .igs and .iges?
No. They are the same format and the same reader handles both; the extension just reflects what the exporting program chose to write.
My mesh has holes or my slicer says it is not watertight. Why?
IGES describes a part as individual trimmed surface patches, and this conversion does not sew them before tessellating, so neighboring patches can leave slivers along their shared edges. Run the repair or auto-fix tool in your slicer, or a dedicated mesh repair tool, and the usual result is printable. A STEP file of the same part tessellates into closed shells and avoids the problem.
Can I choose the mesh resolution or facet count?
Not on this page. Tessellation is fixed at a 0.1 mm absolute chord tolerance and a maximum facet angle of about 29 degrees, the same for a 5 mm pin and a 500 mm housing. If you need a specific triangle budget or a finer angular setting, export STL from a CAD program where you control those values.
The conversion said it could not read my 3D file. What causes that?
Usually a truncated IGES whose terminate section is missing, which happens with interrupted downloads and aborted exports, or a file that is not IGES at all. Re-download or re-export it. A native SolidWorks .sldprt or Inventor .ipt renamed to .igs is refused as well, with the same generic wording on screen.
It said no valid 3D geometry was found, but the file opens in my viewer.
Viewers happily show curves and points, which cannot be meshed. If your IGES holds only wireframe geometry, re-export it with surfaces or solids; if it is a structure file pointing at external part files, export a self-contained version. Curve-only files can still be converted to DXF, where curves stay curves.
My conversion timed out. What should I do?
Each conversion gets ten minutes of engine time, and the rare timeout comes from models with enormous numbers of surface patches rather than from large file sizes. Split the model into fewer bodies per file, remove geometry you do not need to print, or export a STEP solid of the same part, which tessellates faster.
Will colors, layers or part names survive?
No. STL stores triangles only, and this reader takes geometry without names, colors or structure, so the output is one unnamed, uncolored mesh object containing each body as its own shell.
What happens to my file after converting?
Everything runs on our servers rather than in your browser. The uploaded IGES is deleted as soon as the job finishes its last attempt, and the STL stays available for download for about four hours before automatic deletion. Transfers go over HTTPS and the download link is a random token; file names, sizes and conversion outcomes are recorded in our logs, and signed-in accounts keep a history entry.