Convert SLDPRT to STP
This is the export to use when the file is going to another engineer rather than to a printer. STEP keeps the exact curved surfaces instead of flattening them to triangles, and every CAD program on earth reads it.
We cannot read .sldprt files — the format is closed, so the STEP export has to happen in SolidWorks. Once you have the STEP file we can convert it to anything: this page is about getting it out of SolidWorks, not about what to do next.
Exporting a STEP file from SolidWorks
Open the part and start a Save As
File → Save As…
The same route as every other export in SolidWorks. There is no separate Export menu for this.
Choose the STEP type
Save as type: STEP AP214 (*.step;*.stp)
SolidWorks offers AP203 and AP214, and sometimes AP242. Choose AP214 unless you have been told otherwise — it carries colour and is read by everything.
AP203 is older and carries geometry without colour. AP242 is the current standard and adds product manufacturing information, but support for it is less universal. AP214 is the safe middle.
Check the options
Options… → Output as: Solid/Surface geometry
Solid geometry is what you want for a part that is a solid. Exporting as surfaces gives the recipient a set of unstitched faces they have to knit back together, which is work you can save them with one dropdown.
Save, and check the file size
OK → Save
A STEP file is plain text and large — several megabytes for a moderately complex part is normal, and it compresses to a fraction of that if you need to email it.
Why STEP rather than STL
An STL is triangles. It is the right answer when the next thing that happens is printing, and the wrong answer for almost everything else, because the moment a curve becomes triangles the fact that it was ever a curve is gone.
STEP stores the actual geometry: a cylinder as a radius and an axis, a fillet as a real blend surface, a spline as a spline. The recipient can measure it exactly, machine from it, cut a section through it, or use its faces as references for their own design. None of that works reliably from a mesh.
It also carries an assembly tree with named components, the units, and a tolerance describing how accurately the surfaces meet. An STL carries none of those.
The one thing STEP does not carry is the feature history. The recipient gets the finished shape as exact surfaces, not your extrudes and cuts — so they cannot change a dimension and have it rebuild. That is deliberate: the feature history is specific to SolidWorks, and STEP is a format for exchanging shapes between programs that model in different ways.
AP203, AP214 and AP242
These are application protocols — subsets of the STEP standard aimed at different jobs. All three describe the same kind of geometry and any program that reads one reads the others.
AP203 is the oldest and the most conservative. Geometry and assembly structure, no colour. Choose it only if the recipient specifically asks, or if something in their pipeline is old enough to be fussy.
AP214 adds colour and a few other presentation features, and it is what most CAD programs default to. It is the safe choice for almost every situation.
AP242 is the current standard and merges AP203 and AP214, adding product manufacturing information — tolerances and annotations carried as data rather than as drawings. It is the right answer where both ends support it, and support is good but not universal.
If you do not know what the recipient uses, send AP214. If they come back and say their software will not open it, AP203 is the fallback.
What we will and will not be able to do with it
Reading STEP needs a CAD kernel — the same kind of software that sits underneath SolidWorks or FreeCAD — because the file describes surfaces mathematically rather than as triangles. That is a large piece of software, and building it into this site is work in progress.
When it lands, STEP to STL will be a real conversion with a tessellation setting, the same way SolidWorks does it. STEP in the other direction is a separate problem: writing a STEP file from a mesh means wrapping thousands of triangles as flat faces, which produces a valid file that no CAD program enjoys.
In the meantime, FreeCAD reads STEP, is free, and exports STL. That is the route to use today if you have a STEP file and need a mesh.
Questions
- Is .stp the same as .step?
- Yes. Two extensions for the same format, because older systems wanted three-letter extensions. Nothing about the contents differs.
- Which STEP version should I choose?
- AP214 unless told otherwise. It carries colour and everything reads it. AP203 is the fallback if the recipient’s software is old; AP242 is the current standard where both ends support it.
- Does STEP keep my feature tree?
- No. You get the finished shape as exact surfaces, not the extrudes and cuts that produced it. That is what STEP is for — exchanging shapes between programs that model in different ways.
- Why is my STEP file so large?
- It is plain text describing every surface mathematically. Several megabytes is normal. It compresses extremely well, so zip it before emailing.
Where to go next
Related guides
Tools that do part of this here
About these formats
Checked against current software versions on 2026-09-11