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Convert STL to STEP in Your Browser

CAD programs such as Fusion 360, SolidWorks, Onshape and FreeCAD prefer STEP files, while printers and scanners give you STL meshes. This page turns the triangles of an STL into a STEP body: flat neighbouring triangles are merged into larger faces, edges are shared, and a closed mesh becomes a real solid you can measure, cut and add features to. Be clear on one thing: the result is faceted. Curves stay made of flat facets and are not rebuilt into smooth NURBS surfaces.

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How to use it

  1. 1

    Add your STL

    Drop a binary or ASCII .stl on the box or click to pick it. The preview shows the mesh and whether it is closed.

  2. 2

    Pick the unit

    STL has no unit field. Choose millimetres or inches to match how the STL was made; the STEP file records that unit so CAD opens it at the right size.

  3. 3

    Merge flat faces

    Leave merging on to join coplanar triangles into one face each, which gives a lighter file and cleaner flat faces in CAD.

  4. 4

    Download the STEP

    Save the .step file and open or import it in your CAD program. The panel says whether it was written as a solid or as an open surface.

What to know before you convert

  • The STEP is faceted: every flat region of the mesh becomes one planar face. Curved areas stay as many small facets and are not turned into smooth cylinders or NURBS.
  • Only a closed (watertight) mesh becomes a solid body. A mesh with holes is written as an open surface body, and the page tells you so before you download.
  • Meshes above 25,000 triangles are refused, because faceted STEP files that size are huge and very slow in CAD. Reduce the triangle count first with the STL file size reducer.
  • Colours, textures and multiple bodies are not carried over; the whole STL becomes one body.

STL to STEP: Using FreeCAD vs This Page

The classic free method is FreeCAD: open the STL, switch to the Part workbench, run Create shape from mesh, then Convert to solid, then export the result as STEP. It works, but it means installing a CAD program and learning where those commands are.

This page does the same steps in your browser: it builds a shape from the mesh, merges flat neighbouring triangles into single faces, and writes a solid when the mesh is closed. The result is the same kind of faceted solid that FreeCAD makes, ready to import into Fusion 360, SolidWorks, Onshape or FreeCAD itself.

What You Can and Cannot Do With the Result

You can measure it, place it in an assembly, cut holes and pockets, add bosses and mounting tabs, and combine it with other bodies. That covers most real jobs: a mount for a 3D-scanned part, a case around a downloaded model, or a fix to a printable part whose CAD file is lost.

You cannot edit the original design history, and curved areas stay faceted, so a fillet or a round surface cannot be changed with one parameter. If the mesh has too many triangles, reduce it first with Reduce STL File Size. To check a STEP file someone sent you, use the STEP Viewer, and to go back to a printable mesh, use STEP to STL.

Don't have a model?

Generate one from a sketch, image or text. Our AI generators give you a 3D model with an STL download for printing. They use credits; this converter does not.

Sketch to STL →Draw it, get a printable model.Image to STL →One photo of an object.Text to STL →Describe it in a sentence.

Frequently Asked Questions

No. An STL only stores triangles, so there is no curve information to recover. Each flat area becomes one face, and curved areas stay as facets. That is enough to measure, add holes, cut and combine with other parts, but a cylinder will not show up as a true cylinder. Rebuilding smooth surfaces needs reverse-engineering tools.
A solid needs a closed mesh: every edge must be shared by exactly two triangles. If the STL has holes or loose edges, the page writes an open surface body instead and says so. Repair the mesh in your slicer or mesh tool, then convert again to get a solid.
Yes. The file is standard STEP AP214 with planar faces, which all of them import. In Fusion 360 and SolidWorks a closed mesh arrives as a solid body you can add features to.
Every triangle turns into a face with its own edges and loops, so the STEP is many times bigger than the STL and CAD programs slow down a lot. Reduce the mesh first; for most parts a few thousand faces are plenty.
The one the STL was made in. Most printing models are in millimetres. If the part opens 25.4 times too big or too small in CAD, convert again with the other unit.
Open the STL, go to the Part workbench, choose Part > Create shape from mesh, then Part > Convert to solid on the new shape, and export it as STEP. This page does the same steps in your browser and also merges flat triangles into larger faces, with nothing to install.
Yes. STP is just another extension for the same STEP format. Save the file from this page and rename it to .stp if your software asks for that extension; the content is identical.
No. The page reads the file and converts it inside your browser with the open-source three.js library. Nothing is sent to our servers, there is no account, and no credits are used. Closing the tab discards everything.