How to Convert STEP to STL (and When You Don’t Need To)
Convert STEP to STL in Fusion 360, SolidWorks, Onshape or FreeCAD with the right tolerance settings, or skip it and upload the STEP file directly.
STEP is how engineers share CAD models, but STL is what most 3D printers and slicers expect. If you've been sent a .step or .stp file and want it printed, you need to turn it into an STL (or 3MF) first. That takes about a minute in most CAD tools. This guide covers how to do it in the common tools, the export settings that matter, and the shortcut: if you're printing with us, you can upload the STEP file directly and skip converting altogether.
STEP vs STL: What's the Difference?
They describe geometry in fundamentally different ways:
- STEP (.step, .stp) stores exact geometry. A hole is a true circle, a fillet is a true curve, and the file knows which faces are planes, cylinders or splines. It's the standard exchange format between CAD programs and can hold whole assemblies.
- STL (.stl) stores only a surface made of flat triangles. Curves are approximated by many small facets. It has no units, no colours and no concept of separate parts. More detail is in STL vs 3MF.
Converting STEP to STL is called tessellation: the software places triangles over every curved surface. The only real decision is how fine those triangles should be.
The Settings That Matter
Most tools expose two tolerances, sometimes behind a "Refinement" or "Options" button:
| Setting | What it controls | Good value for FDM printing |
|---|---|---|
| Chord / surface deviation | How far a facet may sit from the true curve | 0.01–0.05 mm |
| Angular deviation / normal deviation | The maximum angle between neighbouring facets | 5–15° |
| Format | Binary or ASCII STL | Binary (much smaller) |
| Units | Millimetres or inches | Millimetres |
A layer of FDM plastic is typically 0.2 mm tall and a nozzle is 0.4 mm wide, so deviations much below 0.01 mm won't show up in the print. They just make the file bigger. Going the other way, a coarse export turns small holes into visible polygons and can make press-fits too tight.
How to Convert in Common Tools
Fusion 360
Open the STEP file (it imports as a design), then right-click the body or component in the browser and choose Save As Mesh. Set the format to STL (binary), units to millimetres, and refinement to "High" or a custom surface deviation of about 0.02 mm.
SolidWorks
Open the .step file, then use File → Save As and choose STL. Click Options and set Resolution to "Fine" or "Custom", Output as binary, Units to millimetres. For assemblies, tick "Save all components of an assembly in a single file" if you want one mesh.
Onshape
Import the STEP file into a document, right-click the part in the Part Studio, and choose Export. Pick STL, binary, millimetres, and resolution "Fine".
FreeCAD (free)
Open the STEP file, switch to the Mesh Design workbench, and use Meshes → Create mesh from shape. Choose "Standard" with a surface deviation of about 0.02 mm and angular deviation of about 10°, then export the resulting mesh as STL.
Bambu Studio, PrusaSlicer and OrcaSlicer
Recent versions of these slicers can import STEP directly and tessellate it for you. If you only need a print, you may not need a separate conversion step at all.
What About Online Converters?
Free online STEP-to-STL converters work for simple parts. Keep two things in mind. First, you're uploading your design to a third party, which may not be acceptable for client or work files under an NDA. Second, most don't expose the tolerance settings, so small features can come out coarse. For anything confidential or precise, use a local CAD tool.
Common Problems After Conversion
- The model is tiny or huge. The export used inches, or the file was interpreted as metres. A part that is exactly 25.4× too small was exported in inches. Our quote page catches this and offers a one-click fix.
- Visible facets on curves. The tolerance was too coarse. Re-export with a smaller chord deviation.
- A huge file. The tolerance was too fine. Anything over about 50 MB for a single part is usually overkill.
- Gaps or non-manifold errors. These usually come from surfaces that never formed a closed solid in the original CAD. Fix them at the source if you can. Our guide to preparing STL files covers mesh repair.
- Assembly parts fused together. Exporting an assembly as one STL merges everything into a single mesh. Export parts separately if they need to be printed separately.
Or Skip the Conversion Entirely
If the goal is a printed part, you don't need to convert at all. Our quote page accepts STEP and IGES files directly, alongside STL, 3MF and OBJ. We tessellate the file on our side at settings tuned for our printers. If you upload an assembly, we split it into its individual parts and price each one, so you can see exactly what every component costs. The same works for a ZIP of several files.
Uploading the STEP file also avoids unit mistakes, because STEP carries real units and we read them directly. Files up to 100 MB are accepted.
Got a STEP file from your CAD package or a supplier? Drop it on the quote page. No conversion needed.
