Convert 3DM to STEP
Convert 3DM to STEP. This is the one conversion on this site that runs on a server, because rebuilding a solid from triangles needs more than a browser can do. Your file is deleted within an hour.
Result
Before you convert: what this keeps and what it destroys
Preserved
- The shape, as planar faces built from the triangles
- Overall dimensions and proportions
- Watertightness, where the input is watertight
- The unit, recorded in the file
- Colour
- Separate parts and their positions
Destroyed
- Cones, spheres, tori and NURBS, rebuilt as planar facets
Why people convert 3DM to STEP
Rhino exports STEP itself, and if the licence is in front of you that is the better path by a wide margin: it converts the NURBS surfaces exactly. This page is for the times you have been handed a .3dm and do not have Rhino.
Understand what is being converted. This site reads the render mesh that Rhino saved for display, not the underlying NURBS, and the STEP is rebuilt from those triangles as planar faces. Rhino's default meshing is tuned for how a model looks on screen, so a curved surface can arrive noticeably coarse, and the faceting you get is whatever the person who saved the file happened to have set.
The unit is right, at least. 3DM records its unit system, so the STEP declares the size the model was actually built at.
What you get
You get a plain-text STEP file you can open in an editor containing a boundary representation: planar faces, shared edges and, where the input was closed, a closed shell that CAD software will treat as a solid. Triangles that lay in the same plane are merged into single faces, so a flat side that arrived as two hundred triangles leaves as one face.
Carried across: the unit, recorded in the file, supported base or vertex colour, the supported part structure.
This conversion runs on a server. The upload is deleted within an hour, and nothing about you is recorded alongside it: no IP address, no filename, no account.
What to check afterwards
- 3DM declares its unit in the file. Check the output dimensions in the receiving application, especially when its import settings can override the unit.
- This is a reconstruction, not a recovery. Coplanar triangles are merged into planar faces and the result is a real solid, but cones, spheres, tori and NURBS surfaces are not recovered and there is no feature tree. Use it as reference geometry.
If you need something this conversion cannot give you
If you need a parametric model, use the original CAD file or remodel the part using this output as reference. Surface fitting can create new geometry, but a mesh does not contain the original sketches or feature history.
Going the other way
This site reads 3DM but does not write it. For the reverse conversion, use an application that can export 3DM.
How we know this conversion works
This pair was checked against 3 files from the test corpus on 2026-09-04. 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.