Convert STL to STEP

Can I convert an STL to STEP?

Yes. This page does it for free, with no account, and the result is a STEP solid you can open in CAD software. Two things limit it. The mesh can have at most 40,000 triangles, and the STEP is rebuilt from those triangles, so it has flat faces, not the curved surfaces of the original design.

Check the size before you upload

The limit is on triangles, not megabytes. A binary STL takes 50 bytes per triangle plus an 84-byte header, so 40,000 triangles is about 2 MB. Open the file in the STL viewer first: it reports the triangle count and whether the mesh is watertight. A binary STL over the limit is refused before anything is stored.

Nothing on this site reduces a mesh. If yours is larger, reduce the triangle count in a mesh tool first, or ask whoever made the part for a STEP export of the original CAD.

What you get

The STEP is in millimetres, because an STL has no unit and this converter reads its coordinates as millimetres. Each flat region of the mesh becomes one face, so a 20 mm cube comes out as six faces, not twelve triangles. A cylinder comes out as a ring of narrow flat strips, because that is what the triangles describe. Separate pieces become separate shells.

If the mesh has holes, the file is written as an open surface model rather than a solid, and CAD software may treat it as a surface. Check for open edges in the STL viewer before you convert.

What to check afterwards

• Compare one dimension you know against the STEP in your CAD program.
• Check whether the body imported as a solid or as a surface.
• Expect curved parts to arrive as many narrow faces.
• Keep the STL. Converting back gives you triangles, not the original surfaces.

Questions people ask

Can I convert an STL file to a STEP file? Yes, within the limits above.

Are STEP files better than STL? They hold different things. A STEP exported from CAD stores exact surfaces, so holes stay round and dimensions can be edited. An STL stores triangles only. A STEP made from an STL has flat faces built from those triangles, so it is closer to the STL than to the original CAD file.

Can I convert an STL to STEP online for free? Yes. It is free, needs no account, and uploads the file. One address can start ten conversions an hour.

Can you edit the STEP file after conversion?

The output can provide a solid or surface reference for CAD work, depending on the input mesh. A CAD application's direct editing tools may let you change some faces. You will not receive the sketches, constraints or feature history used to design the original part.

This converter rebuilds faces from the STL triangles and merges compatible coplanar faces. A flat side can become one face. A curved wall remains faceted because the converter does not fit a new cylinder or NURBS surface to it.

When to ask for the original CAD file

Ask for the native model or a STEP export from it when you need to change a hole diameter, check an exact curved surface or continue parametric design. Specialist reverse-engineering tools can fit new surfaces to a mesh, but that is a modelling operation with assumptions and tolerances. It is not recovery of the original design history.

Before converting, check the mesh in the STL viewer. An open mesh may produce an open shell instead of a closed solid. Check the dimensions too: the conversion assumes STL coordinates are millimetres and records that unit in the STEP output.

This conversion runs on a server. The download link expires after one hour, and an automatic storage rule then deletes the upload and the result; the storage service says it typically removes expired files within 24 hours. The job record holds no IP address, no filename and no account.

Going the other way

Convert STEP back to STL is the reverse page. It is not the inverse of this one: reconstructing a solid from triangles produces faceted geometry, and tessellating it again would not return you to where you started.

How we know this conversion works

This pair was checked against 8 files from the test corpus on 2026-09-07. Each run parses its own output back in and compares the bounding box, the triangle count and, for closed solids, the volume against the input.

A pair that fails those checks doesn't get a page. That's why this site lists 120 conversions and not the several hundred a format-times-format grid would suggest.