nozzlefox

STLSTEP

STL to STEP converter

Turn an STL, OBJ or 3MF mesh into a STEP solid for your CAD program, with flat areas as real faces.

  • Nothing uploaded
  • No sign-up
  • Free, no limits

Drop your STL, OBJ or 3MF here

or paste it, or pick it from your device

.stl · .obj · .3mf

  1. Drop your STL file
  2. Check it in 3D
  3. Download STEP

Good to know

How to convert STL to STEP

  1. Drop your STL, OBJ or 3MF above. You can add more files to combine them.
  2. Flat areas are merged into single faces straight away; the outlines show the faces your STEP file will have.
  3. Untick any parts you don't want, then download the STEP file.

Your files stay on your device; nothing is uploaded.

What you get

A mesh is only triangles, so the converter rebuilds faces from them. Neighbouring triangles that lie in the same plane become one flat face, and straight runs of edges become one edge. A box exported as 12 triangles comes back as 6 faces and 12 edges, just as if it had been modelled. Each part becomes a solid body (or a named body in an assembly when there are several), with its colour if it had one.

Curved surfaces can't be recovered this way: a cylinder stays a ring of narrow flat faces, and a hole is a polygon. That's fine for most jobs:

  • Measuring, and adding holes, cuts, mounts or text in Fusion, SolidWorks, Onshape or FreeCAD.
  • Moving or offsetting flat faces with direct-editing tools.
  • Sending a model to someone who only accepts STEP.

To edit a curved feature itself (change a hole's diameter, a fillet's radius), the part has to be remodelled; the faceted body makes a good reference to trace over.

Units and size

STL files have no units. The STEP file is written in millimetres, taking the STL's numbers as mm, which is what slicers and nearly every 3D printing site use. If the model opens 25.4 times too small, it was drawn in inches: scale it by 25.4 in your CAD program.

Why big meshes make big STEP files

Every face in a STEP file carries its plane, edges and corners, so curved areas cost roughly half a kilobyte per triangle: a 10,000-triangle figurine becomes a STEP file of about 5 MB. CAD programs also slow down with tens of thousands of faces. For scans and sculpts, reduce the triangle count first, or keep working with the mesh: Fusion, SolidWorks and FreeCAD can all import STL directly as a mesh body.

Have a STEP file and need a mesh? Use STEP to STL. Mesh has holes? Run it through Repair STL first; small holes are filled automatically here too.

Questions

Can I convert STL to STEP for free?

Yes. Drop the file into the converter at the top of this page and download the STEP. There's no sign-up, no limit and nothing is uploaded.

Will the STEP file be editable in Fusion or SolidWorks?

It opens as a solid body you can cut, drill, add features to and measure, and its flat faces can be moved. Curved areas stay as many small flat faces, so changing a hole's size or a fillet means remodelling that feature.

Why is my STEP file so much bigger than the STL?

STEP describes every face with its plane, edges and corners, which takes much more text than a triangle. Flat areas merge into few faces and stay small; curved and organic shapes keep one face per triangle.

Does it work with OBJ and 3MF files too?

Yes. OBJ and 3MF meshes convert the same way, and each object in a 3MF becomes its own named body.

Which STEP version is the file?

AP214 (automotive design), the version most CAD programs read and write by default. Fusion, SolidWorks, Onshape, FreeCAD, Inventor and Rhino all open it.