Convert STEP to OFF Mesh
Give the converter a STEP or STP model and you get back an ASCII OFF file: a list of vertices in millimeters followed by a list of triangles that share them, without colors or normals. The mesh is cut from the CAD model's exact geometry, so curved faces deviate from it by 0.1 mm at most.
Download Started!
How would you rate your experience with MiConvert?
Why Convert STEP to OFF
OFF (Object File Format) is about as simple as a mesh format gets: the word OFF, a line with the vertex and face counts, the vertex coordinates, then one line per face listing vertex indices. It comes from Geomview and is still a default input for geometry-processing code, including CGAL examples, libigl, MeshLab and the ModelNet datasets used in 3D deep learning. STEP is the opposite, exact boundary geometry for CAD-to-CAD exchange, and none of those tools read it.
The conversion runs on our server in two stages inside FreeCAD 1.1. First FreeCAD reads the STEP through OpenCASCADE and tessellates every face with a fixed 0.1 mm deviation and a 0.5 radian angle limit. The resulting triangles are then loaded into trimesh, a Python mesh library, which merges coincident vertices and writes the OFF file.
Because vertices are merged, neighboring triangles reference the same vertex indices along shared edges, the way an indexed mesh should, unlike STL where every triangle repeats its own corners. All faces are triangles. Coordinates are in millimeters, with STEP files in inches or meters scaled on import. There is no color or normal data, and an assembly arrives as one combined mesh in which each body is still a separate shell at its modeled position.
This is a rare pair compared with STEP to STL. It mostly serves people building a dataset from CAD parts or feeding a mechanical part into research code that reads OFF. If your tool also accepts STL, OBJ or PLY, those are equally valid outputs from the same STEP; the tessellation is identical and only the file layout differs.
How to Convert STEP to OFF
- Export the part or assembly from your CAD program as STEP. Delete bodies you do not want first, since every body in the file ends up in the OFF.
- Select your STEP file here; OFF is preselected as the target.
- Click Convert and wait for the download link.
- Load the OFF in your tool. If it expects meters or a unit cube, rescale after loading, because the coordinates are in millimeters.
- For learning pipelines, normalize or resample in your own code: the CAD tessellation is kept as is, so triangle sizes range from long flat strips to tiny fillet facets.
Output Format Details
- ASCII OFF with a vertex and face count header, readable by any OFF parser
- Indexed triangle mesh with merged vertices, so faces share edges
- Tessellated from the exact STEP surfaces by FreeCAD 1.1 at a 0.1 mm deviation
- Millimeter coordinates, with inch and meter STEP files scaled on import
- Curve-only STEP files refused instead of producing an empty OFF
Video Tutorial
STEP → OFF in seconds! Free online converter at MiConvert.com 🔗 https://miconvert.com/en/step-to-off?utm_source=youtube&utm_medium=social&utm_campaign=step-to-off Quick steps: Upload → Convert → Do
Frequently Asked Questions
Is STEP to OFF actually supported?
Yes. OFF is listed as a target for STEP in the converter's capability table, and the job runs the same FreeCAD reader as STEP to STL before trimesh writes the OFF. It is simply an uncommon request.
Does the OFF file contain colors or normals?
No. Only vertex positions and triangle indices are written. Per-face colors are optional in OFF and none are added, and the STEP's own colors are not read in the first place.
Are the faces triangles or the original polygons?
Triangles. STEP faces are curved, trimmed surfaces with no polygon equivalent, so they are tessellated; even a flat rectangular face becomes two triangles.
Why is the triangle size so uneven?
The tessellator only adds triangles where curvature needs them, so big flat faces become a few long triangles while fillets get many small ones. Remesh in MeshLab or in your own code if your method needs uniform triangles.
Why was my STEP file rejected?
Either it is not valid STEP, because the ISO-10303-21 header is missing or the file was cut off, or it has no surfaces, for example a wireframe or an assembly that only references other part files. Export one STEP with the solid geometry included and try again.
Can I convert OFF back to STEP?
Not here, and not exactly anywhere: a mesh holds no exact surfaces to recover. MiConvert turns OFF into other mesh formats, DXF and 3DM, but STEP is not an output for it.
Where is the conversion done, and is my file kept?
On our servers. The STEP you upload is removed when the job finishes, and the OFF is cleared automatically roughly four hours later. Without an account the size limit is 50 MB per file.