What a faceted STEP gives you
The converter takes each triangle of the mesh and writes it as a planar face. Neighboring faces share edges, the closed shell becomes a solid, and your CAD program receives a body instead of a loose cloud of triangles.
What it cannot do is recognize features. A hole stays a ring of narrow flat strips, a fillet stays a staircase of facets, and you cannot pick a cylinder axis or change a radius. Turning a mesh into a true feature-based model needs remodelling, and that work happens in CAD.
File size: about 1 KB per triangle
A faceted body is large: plan for roughly 1 KB per triangle. Open Info before converting and read the triangle count to know what you will download.
Scanned or sculpted meshes often carry far more triangles than the shape needs. Edit → Reduce triangles cuts them to a percentage you choose; in our test a sphere reduced to 30 % kept its volume within 2 %. The STL simplifier page walks through it.
Units before you convert STL to STP
An STL file stores no units, only numbers. The viewer shows them as millimetres, and the STEP is written with those values. If the part was drawn in inches it will look 25.4 times too small. Use Edit → Inches → mm (×25.4) first, or set an exact size with scale STL, then convert.
Steps from STL file to STEP file
- Drop the .stl or press Open File.
- In Info, check the size in mm, the triangle count and whether the mesh is watertight.
- If the check lists holes or open edges, run Edit → Repair, since a closed shell is what becomes a solid.
- Press Download STEP.
- Open the result in the STEP viewer to confirm it reads back.
How big the STEP will be: a worked example
A binary STL spends 50 bytes on each triangle after an 84-byte header. Our 9,024-triangle test sphere is 451,284 bytes as STL. Written as a faceted STEP at about 1 KB per triangle, the same sphere comes to roughly 9 MB, around twenty times the STL.
Run the same sum on your own file before you press the button: triangles from Info, times 1 KB. A 200,000-triangle scan lands near 200 MB, a heavy file to send and to import. Reduce it first, look at the shape again, and convert after that.
If the STEP will not import as a solid
An STL with holes gives an open shell, and CAD may import it as loose surfaces. Read the mesh check before converting: Watertight should say yes, with 0 open edges and 0 non-manifold edges. The Repair in Edit panel button under the check opens the fixer, and Repair mesh runs it.
If the body imports inside-out, look at the Normals line; Repair turns them outward. A file that still fails is worth checking in the STEP viewer here first, so you know whether the problem is the file or the import settings of your CAD program.
What we tested and what we have not
A 20 mm cube converted to STEP and re-opened with the same size, volume and triangle count. A 9,024-triangle sphere went through STL → STEP as well, and OpenCascade read it back with every triangle in place.
We have not yet opened these files by hand in desktop CAD programs. Treat the output as a solid reference body and check it in your own CAD before you build on it. The STL never leaves your device during any of this.
Other directions from the same mesh
For a slicer, STL to 3MF stores the part in millimetres. For rendering tools, STL to OBJ keeps the triangles as they are. Going the other way, STEP to STL tessellates a real CAD file with a precision you pick.
Questions and answers
Can you convert STL to STEP?
Yes, as a faceted solid: the triangles become flat faces of a closed body. You get a STEP that CAD can import as a body, without cylinders, fillets or editable features.
Why is the STEP so much bigger than the STL?
Every triangle becomes a separate face record in the STEP, and each one takes about 1 KB. Reduce triangles first if the mesh is dense.
Is STL to STP the same as STL to STEP?
Yes. STP is the short extension of the same format, and the download works for either name.
Can I convert a batch of STL files?
Not yet. The page converts one file at a time; press Convert another file for the next one.
Does the converter recognize holes and fillets?
No. Feature recognition is not part of the tool, so every curved surface stays as flat facets. Remodel those features in CAD if you need to edit them.
What size will the part have in CAD?
The same numbers you see in Info, where the viewer shows them as millimetres. An STL drawn in inches needs Edit → Inches → mm before the conversion, or the body arrives 25.4 times too small.