Convert IGS to STP (STEP)
Honest status first: this particular page's uploader rejects every file with a "conversion impossible" notice, because the three-letter target .stp is not matched against the IGES format's registered target name. Use our IGS to STEP converter instead, then rename the downloaded .step to .stp if your software insists on the short extension.
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IGES, STEP and why the two extensions confuse people
IGS (also written .iges) is the file extension of IGES, the surface exchange standard that predates STEP. An IGES file describes a part as a collection of trimmed surface patches, type 144 entities, with no requirement that those patches be stitched into a closed solid. Many modern CAD seats have pushed IGES import to the back of the list or dropped it, while nearly all of them still read ISO 10303 STEP, which is why suppliers and machine shops keep asking for a .stp.
.stp and .step hold the same Part 21 text; the short form is only an old Windows filename habit. That matters here because of the bug: this landing page locks its target to the literal string "stp", the IGES format registers its exact-geometry target as "step", and the check that runs in the browser compares the two and refuses the upload before anything is sent. The server side would accept the job, so the engine is fine and only this page's file picker is not. Nothing runs in your browser either: both pages queue the work on our servers.
What the conversion does when you run it through the IGS to STEP page: FreeCAD 1.1, built on Open CASCADE 7.9, reads the file with Part.Shape.read and writes it with exportStep, producing an AP214 (AUTOMOTIVE_DESIGN) file with units declared as millimeters. The geometry stays exact B-rep, so nothing is tessellated. Transport damage is repaired first: gzipped files are unpacked, UTF-16 text is re-encoded, a stray byte-order mark is stripped, and a file that is actually a ZIP, a PDF or a native SolidWorks or Inventor document is detected and refused rather than half-parsed, though the on-screen text is the generic "Could not read this 3D file" message rather than a named reason.
The one thing to plan for is sewing. Because IGES faces arrive as independent patches and nothing stitches them, the STEP you get back contains one open shell per face rather than a solid; in testing, a 42-face part came out as 42 open shells and zero solids. That is still fine for reference, measurement and most CAM setups, but for a watertight solid you will need your CAD system's Sew, Knit or Heal command after import. Names, colors, layers and any assembly tree are not read at all, so the STEP is pure geometry under one generic product entry.
How to get a .stp from your IGS today
- Open our IGS to STEP converter page, since this page's file picker blocks the upload.
- Check the file is a complete IGES export. A truncated file missing its terminate section is reported as unreadable, and a structure-only IGES that just references external parts through type 416 entities contains no geometry to convert.
- Upload the .igs or .iges file. Limits are 50 MB per file as a guest, 100 MB with a free account, 200 MB on Plus and 1 GB on Pro, with 10 files per batch (25 on Plus, 50 on Pro).
- Download the STEP file; links stay live for about four hours.
- Rename the extension from .step to .stp if the receiving program or supplier portal only accepts three letters. The contents are unchanged.
- After importing, run Sew, Knit or Heal on the surfaces if you need a closed solid for machining or simulation.
What the IGES to STEP engine does
- Exact B-rep passthrough: surfaces and curves are rewritten as STEP geometry, with no meshing and no chord tolerance involved
- Writes AP214 AUTOMOTIVE_DESIGN with SI millimeter units, the dialect most CAD and CAM importers expect
- Accepts both .igs and .iges, and repairs gzip wrappers, UTF-16 encoding and a leading byte-order mark before reading
- Checks the file signature before parsing, so ZIP, PDF and native SolidWorks or Inventor files renamed to .igs are rejected rather than half-converted (the on-screen message is the generic "Could not read this 3D file" text)
- Can also target meshes from the same IGES file if you need STL, OBJ, 3MF or GLB downstream
- Runs server-side with no CAD installation on your machine, and no account needed for files within the guest limit
Video Tutorial
Are you struggling with how to convert your IGS file to STP format? Don't worry, in this video I will reveal a super convenient tool to help you change your file extension completely for free without
IGS to STP questions
Why does this page refuse my file before uploading?
The target on this page is registered as "stp", while the IGES format's exact-geometry target is registered as "step". The check that runs in your browser compares those two strings, finds no match, and shows a conversion-impossible notice. It is a naming mismatch on our side, not a problem with your file. Use the IGS to STEP page, which passes the same job to the same engine.
Is .stp a different format from .step?
No. Both are ISO 10303 Part 21 text. Renaming the downloaded .step file to .stp is safe and does not alter a single byte of geometry.
Will the STP contain a solid body?
Usually not. IGES stores separate trimmed surface patches and the conversion does not stitch them, so the output is one open shell per face with no manifold solid. Use Sew, Knit or Heal in SolidWorks, Fusion 360, Inventor or FreeCAD to close it, and expect to patch gaps where the original surfaces did not meet cleanly.
Is the conversion lossless?
The surface geometry itself is exact, since nothing is tessellated. Everything else is dropped: part names, colors, layers and assembly structure are never read, and the header carries a generic Open CASCADE translator product name instead of your part name.
I searched for a 100 MB or 2 GB limit. What do you actually accept?
50 MB per file as a guest, 100 MB with a free account, 200 MB on Plus and 1 GB per file on Pro. There is no 2 GB single-file option, so split a very large assembly into part files and convert them one by one.
Can I convert IGS to STL instead?
Yes, IGES can go to STL, OBJ, PLY, 3MF, OFF, GLB and other mesh targets, tessellated at a fixed 0.1 mm chord tolerance and roughly 29 degrees of angular deviation. Because the IGES faces are not sewn, the resulting STL can have cracks and may not be watertight enough for slicing without repair.
The result says the file could not be read. What now?
The engine's specific reasons are collapsed into two generic messages, so check the likely causes yourself: the export may be truncated, it may only reference external part files rather than containing geometry, or it may be a native CAD document renamed to .igs. Re-exporting from the source CAD system with geometry included fixes most cases.
How long are my files kept?
The upload is deleted as soon as the job's last attempt finishes. The converted STEP file stays available through a random download link for about four hours, then it is deleted automatically. File names, sizes, formats and outcomes are logged, and signed-in accounts keep a history row.