How to convert STL to STEP with real, editable faces
Last updated by the stl2step team
To convert an STL to a STEP file you can edit, the triangles have to be turned back into CAD faces: planes, cylinders, cones, spheres, tori and smooth B-splines, sewn into one closed solid. stl2step does this automatically with AI in 10 seconds to 2 minutes for a typical part; ordinary converters only wrap each triangle in its own flat face.
Convert STL to STEP in 6 steps
Check that the mesh is closed
A solid needs a watertight mesh: no holes, no gaps, every edge shared by two triangles. Most STLs exported from CAD already are. For scans or downloaded models, run a repair first (for example the mesh repair in your slicer, Meshmixer or Blender's 3D-Print Toolbox).
Keep it under the size limit
stl2step converts meshes up to 150,000 triangles and 50 MB. If yours is denser, decimate it; a few tens of thousands of triangles are plenty for a mechanical part.
Upload the STL
Sign in at stl2step.ai with your email and drop the file (STL, OBJ or PLY). You see the mesh in 3D and the cost, one credit, before you convert. New accounts get 3 free conversions.
Let the AI rebuild the faces
The network decides which triangles belong to the same face, each face gets its exact surface (plane, cylinder, cone, sphere, torus or B-spline), and the faces are trimmed and sewn into one closed solid. Typical parts take 10 seconds to 2 minutes.
Check the result and download the STEP
Switch the viewer between faces and surface types to see what was recovered, then download the .step file. Pro and pay-per-use plans also get a JSON report with every face's type, parameters and fitting error.
Open it in CAD and keep designing
Open the STEP in SolidWorks, Fusion, Onshape, Inventor, Rhino, FreeCAD or any other CAD program. Holes are cylinders you can resize, flat sides are single planes you can move or offset.
STL vs STEP: what changes
An STL stores only triangles: no faces, no edges, no units, no surface types. A STEP file (ISO 10303) stores a boundary representation (B-Rep): a solid made of faces, each one lying on an exact surface, joined along shared edges. CAD programs edit faces, not triangles, which is why the conversion matters.
| STL | STEP from stl2step | |
|---|---|---|
| Geometry | Flat triangles approximating the shape | Exact planes, cylinders, cones, spheres, tori and B-splines |
| Topology | None (a list of triangles) | Faces, edges and vertices of one closed solid |
| A 10 mm hole | Dozens of slivers | One cylindrical face with a radius |
| Editable in CAD | No | Yes, with direct-modeling tools |
| Units | None | Coordinates kept exactly as in the STL |
Why "convert to STEP" in a CAD program is not enough
FreeCAD's shape-from-mesh, Rhino's MeshToNURB, SolidWorks' solid-body import and almost every free online converter do the same thing: each triangle becomes its own planar face. The grip on our home page would arrive as 8,672 faces. stl2step rebuilds it as 364, with a mean deviation of 0.003 mm from the original mesh.
Common problems
- "The mesh is not a closed, manifold surface"
- The STL has holes or non-manifold edges, so no solid can be built. Repair it and convert again; the credit of a failed conversion is refunded automatically.
- The part has the wrong size after import
- STL has no units. stl2step keeps the coordinates exactly as they are in the file, so an STL exported in inches has to be scaled by 25.4 if your CAD program assumes millimeters.
- Many B-spline faces on a scanned part
- Scan noise hides the exact shape, so more regions are fitted as smooth B-splines. Clean or smooth the scan first for more analytic faces.
Questions
Can I convert STL to STEP for free?
Yes. New stl2step accounts get 3 free conversions with the STEP download, no card needed.
Does the STEP file keep the dimensions of my STL?
Yes. The coordinates are kept exactly as they are in the mesh; only the representation changes from triangles to exact surfaces.
Will I get a feature tree?
No. STEP never carries the feature history; you get a solid with exact faces, which you edit with direct-modeling tools or feature recognition.