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STEP vs IGES: Which CAD File Format Should You Use?
STEP and IGES are both neutral CAD formats, so a 3D model can move between programs that cannot open each other’s files. STEP carries a complete solid and is the modern default, while IGES is the older, surface-based standard that most programs still read. Send STEP unless someone asks for IGES by name.
Just need to look inside one? Open it free in the online IGES viewer or the STEP viewer, with nothing to install.
What is the difference between STEP and IGES?
STEP sends a part as one closed solid, so the receiving program knows inside from outside and can machine, measure and edit it straight away. IGES usually sends a set of separate surfaces that the receiver has to stitch back into a solid, and a missing surface or tiny gap can make that fail.
| Compared on | STEP (.step, .stp) | IGES (.igs, .iges) |
|---|---|---|
| Standard | ISO 10303, an international standard | A US national standard |
| First published | 1994 | 1980 |
| Still developed | Yes: Yes, new editions keep coming | No: No, 5.3 (1996) is the last version |
| Typical content | A closed solid | Loose surfaces and curves |
| Assemblies | Yes: Yes, with part names | No: Limited, often flattened |
| Units recorded | Yes: Yes | Yes: Yes |
| Common problem | Few | Gaps when surfaces are stitched |
| Use it for | Machining, quoting, sharing, archiving | Requests by name, legacy software |
What an IGES file holds, section by section, is in what is an IGES file.
What does “neutral format” mean?
A neutral format is a vendor-independent way to describe 3D geometry so any CAD program can read it. Every CAD program saves its own native file type, which usually opens only in that program. STEP and IGES are the two best-known neutral formats for parts.
They are the common language that machine shops, suppliers and collaborators use to exchange 3D parts when everyone runs different software.
Do new CAD programs still work with STEP and IGES?
Yes. Every current desktop CAD and CAM program imports and exports STEP, and almost all of them still import IGES. Export to IGES is often still there but is sometimes tucked behind a legacy or advanced option. Newer browser-based tools tend to support STEP first and IGES second, if at all.
In practice that means STEP is the one format you can count on at the other end. PartWork.ai Studio imports STEP and IGES (along with BREP, DXF, OBJ and STL) and exports STEP for machining; see importing files.
How do STEP, IGES, STL, Parasolid and native CAD files compare?
STEP and Parasolid hold exact solids, IGES holds exact surfaces, STL holds a mesh of flat triangles, and a native file holds the full feature history of the program that made it. Only the native file stays fully editable, and only STEP and IGES are open standards every program reads.
| Format | What it holds | Opens in | Best for |
|---|---|---|---|
| STEP | Exact solids and assemblies | Every CAD and CAM program | Sending parts to anyone |
| IGES | Exact surfaces and curves | Most CAD programs | Legacy requests |
| Parasolid (.x_t) | Exact solids | Programs built on the same geometry engine, and many others | Exchange between those programs |
| STL | A triangle mesh, no units | Every slicer and viewer | 3D printing |
| Native (.sldprt, .ipt, .f3d) | Solids plus feature history | Usually only the program that made it | Your own editing |
A mesh cannot be machined from or edited like a solid, which is why converting an STL back to a STEP is the hard direction. For that choice, see STL vs STEP.
When does IGES still make sense?
Use IGES when a shop or client asks for it by name, when the data is freeform surfaces that were never a closed solid, or when the receiving software is too old to read STEP. In every other case STEP is the safer, cleaner choice.
- A request by name. Some established workflows and older CAM software still expect IGES. If they ask for it, send it.
- Surface-only data. Complex freeform surfaces that were never a closed solid travel well as IGES.
- Legacy software. Very old programs that predate broad STEP support may import only IGES.
Which format should you send a machine shop?
Send a STEP file of the part plus a PDF drawing with tolerances, threads and finish. The STEP gives the shop exact geometry for programming and quoting; the drawing carries what the model does not. Add IGES only if the shop asks for it.
The full checklist is in the best file format for a machine shop. If all you have is the drawing, see how to turn a PDF drawing into a STEP file.
How do you convert an IGES file to STEP?
Import the IGES into a CAD program, let it stitch the surfaces into a solid, check that the result is closed, and export STEP. If gaps remain, the STEP will hold surfaces instead of a solid, so always look at the converted part in 3D before you send it.
The steps and what to check are in the IGES to STEP converter guide.
Frequently asked questions
Is STEP better than IGES?
For almost every job, yes. STEP carries a complete solid with its faces and edges joined, so the receiving program can machine, measure and edit it without repair. IGES usually arrives as separate surfaces that may need stitching. Send IGES only when someone asks for it.
Is IGES obsolete?
It is no longer developed: version 5.3 from 1996 is the last one. It is still widely read, so old files and older programs keep it alive, but new work is exchanged as STEP.
Can I convert an IGES file to STEP?
Yes. Import the IGES into a CAD program, check that the surfaces close into a solid, and export STEP. If gaps remain, the STEP will hold surfaces rather than a solid, so look at the result in 3D before sending it.
Do STEP and IGES files keep units?
Yes. Both formats record the length unit in the file, so a part made in millimetres opens at the right size in a program set to inches. STL does not record units, which is why STL parts sometimes open 25.4 times too big or too small.
Can I 3D print a STEP or IGES file?
Not directly. Slicers for 3D printers expect a mesh, so export STL or 3MF from your CAD program, or convert the STEP to STL first. Keep the STEP as the master copy for edits and machining.
Can you make a clean STEP file without a CAD seat?
Yes. Describe the part you need to PartWork.ai in plain English, get editable solid geometry back, and export it as STEP for machining or STL and 3MF for a 3D printer. Viewing files is free; designing and downloading use credits.
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