Convert SLDPRT to STL
A .sldprt is a SolidWorks part file, and only SolidWorks opens it. The export takes about twenty seconds, and the two settings in the options dialog are what decide whether your curved surfaces print smooth or faceted.
Also asked as convert solidworks files to stl. Same answer, written for the way the question is usually typed.
We cannot read .sldprt files, and neither can any other free tool. The format is closed, undocumented, and changes with every release — there is no parser outside SolidWorks itself. If you do not have SolidWorks, skip to the last section: asking the sender for a STEP file solves this completely.
Exporting an STL from SolidWorks
Written for SolidWorks 2022 and later. The dialog has been essentially unchanged since 2015, so older versions follow the same path.
Open the part and start a Save As
File → Save As…
Not File, Export — SolidWorks puts its mesh exports under Save As, which is why people hunt for an Export menu that does not have what they need.
Choose STL as the file type
Save as type: STL (*.stl)
As soon as you pick it, an Options button appears in the dialog. That button is the whole point of this page — the default settings are adequate rather than good.
Open the options
Options… (button in the Save As dialog)
This opens the Export Options window with the STL settings selected. Everything that affects the quality of your print is in here.
Set the resolution
Resolution: Custom → Deviation Tolerance · Angle Tolerance
Coarse and Fine are presets that scale with the model’s bounding box, which means a small detailed part and a large simple one get treated the same way. Custom lets you say what you actually need.
For a part up to about 100 mm, a deviation tolerance of 0.01 mm and an angle tolerance of 5 degrees produces a smooth surface at a sensible file size. Tightening deviation below about 0.005 mm gains nothing a 0.4 mm nozzle can reproduce and multiplies the triangle count.
Check the units
Output as: Binary · Unit: Millimeters
Binary, always — it is about five times smaller and every slicer reads it. Millimetres, because that is what slicers assume and an STL cannot record the unit to tell them otherwise.
If the part was modelled in inches, this dropdown converts it. Getting it wrong here is the classic way to end up with a part 25.4 times too small.
Preview before you commit
Show STL info before file saving (tick it)
This shows the triangle count and file size after you press Save, before it writes. A part that has turned into four million triangles is telling you the deviation tolerance is far tighter than it needs to be.
Save, then check it somewhere else
OK → Save
Drop the STL into any converter on this site to confirm the measured size matches the part you designed, and that the mesh is closed. It takes a few seconds and catches unit mistakes before they become failed prints.
What deviation and angle tolerance actually do
SolidWorks holds your part as exact mathematical surfaces — a cylinder is a radius and an axis, not a set of flat strips. An STL cannot hold that, so the export has to approximate every curve with triangles, and these two settings control how closely.
Deviation tolerance is the maximum distance between the true surface and the flat triangle standing in for it. Set it to 0.01 mm and no point on your printed surface is more than a hundredth of a millimetre away from where the model said it should be. It controls the fineness of large curves.
Angle tolerance is the maximum angle between neighbouring triangles. It controls small features and tight fillets, where the deviation is tiny in absolute terms but the surface is turning quickly. Five degrees is a good default; below about three the file grows quickly for very little visible gain.
The two work together, and which one is binding depends on the feature. A large gentle curve is limited by deviation; a small fillet is limited by angle. This is why the presets disappoint: Fine on a 200 mm part gives a deviation far looser than a printer can resolve, and Fine on a 10 mm part produces far more triangles than anyone needs.
The practical limit is the printer. A 0.4 mm nozzle laying 0.2 mm layers cannot reproduce a feature finer than roughly 0.1 mm, so a deviation tolerance below about 0.005 mm is describing detail that will never exist in plastic. All it costs you is file size and slicing time.
What is lost, and what that means in practice
Everything except the shape. The feature tree — extrudes, cuts, fillets, patterns, the parametric history that lets you change a dimension and have the model rebuild — does not exist in an STL and cannot be recovered from one. Neither do the sketches, the mates, the custom properties, or the material assignment.
The exact surfaces are gone too, and this is the important one. Your cylinder was a cylinder; in the STL it is sixty flat strips, and the number sixty was chosen at export time. Nothing downstream can make it round again, because the information that it was ever round is not in the file.
That is fine when the STL is the last step before printing, which is the usual case. It is a problem when the STL is being sent to someone who needs to machine it, measure it, or modify it — for any of those, send a STEP file instead. STEP keeps the exact surfaces and every CAD program reads it.
If you do not have SolidWorks
This is the common case, and the answer is better than it sounds. You do not need the .sldprt at all — you need the shape that is inside it, and the person who sent it can give you that in about fifteen seconds.
Ask for a STEP file. The wording that works: "could you send that as a STEP file instead — it is File, Save As, and pick STEP from the list." Every CAD program writes STEP, it keeps the exact surfaces rather than triangles, and it opens in FreeCAD, Fusion 360, Onshape and every free viewer.
If they cannot do that, ask for an STL, which is one menu away from the same place and is enough for printing.
What will not work: free SolidWorks viewers that claim to open .sldprt. Some do, through eDrawings, which is genuinely from the same company and genuinely free — eDrawings will open a .sldprt and can export STL if the person who published the file enabled that permission when they saved it. Many do not enable it. It is worth trying and not worth relying on.
Where we can actually help
Once SolidWorks has given you an STL, everything afterwards runs here in your browser — converting it to 3MF so the units are recorded, checking the mesh is closed, or turning it into a GLB or USDZ to show somebody.
Questions
- Can I open a .sldprt without SolidWorks?
- eDrawings, which is free and from the same company, opens one and can sometimes export STL — but only if the person who saved the file enabled that permission. No other free tool reads the format at all. Asking the sender for a STEP file is faster and always works.
- What resolution should I use for 3D printing?
- Custom, with a deviation tolerance of about 0.01 mm and an angle tolerance of 5 degrees for a part up to 100 mm. Tighter than 0.005 mm describes detail a 0.4 mm nozzle cannot print.
- My part came out 25 times too small.
- The unit dropdown in the STL options was left on inches while the slicer read millimetres. Re-export with Unit set to Millimeters.
- Should I send a colleague an STL or a STEP?
- STEP, unless they are only going to print it. STEP keeps the exact curved surfaces so the part can be machined, measured or modified. An STL has already thrown that away.
- Can I get the SolidWorks part back from an STL?
- Not as an editable model. The feature history and the exact surfaces are gone. You can import the mesh as a faceted solid, which is enough to position or reference against, but not something you can change parametrically.
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