Updated 2026-10-19
To convert 3DM to STEP, drop the Rhino .3dm into the converter below and download the .step. NURBS polysurfaces are translated exactly, so the faces Rhino drew are the faces the STEP holds, and SOLIDWORKS, Fusion 360, Inventor or Creo opens it as geometry. No Rhino licence is needed and 2 solid conversions a day need no account. In Rhino itself, Export Selected as STEP does the same.
2 solid-geometry conversions a day with no account. No card, no install.
On our servers. No account: deleted within 24 hours. Signed in: kept until you delete them. Never shared or used for training.
Trimmed NURBS breps and lightweight extrusions become true surfaces in the STEP output, with nothing tessellated, in millimetres whatever the model's unit. Mesh and SubD objects beside them come too, rebuilt as true surfaces where they fit and facets where they do not. Hidden objects are left out, and the converter says how many.
A 3DM that is all mesh has its surfaces recovered from the triangles where they fit and facets where they do not, and the conversion says which of the two it gave.
Rhino and STEP both describe shape with exact NURBS surfaces, so a trimmed polysurface carries over as the same surfaces, curves and dimensions, with nothing tessellated.
The difference is what the receiving CAD system expects. Rhino will hold open surfaces, loose curves, meshes and solids side by side on layers; a mechanical CAD system wants closed solids. Closed polysurfaces become solids in the STEP. Open ones arrive as surfaces, which most CAD systems will open but not treat as a body, so Join in Rhino and check for naked edges before converting. Every visible object is read, extrusions and block instances included, each as its own body and in the model's unit scaled to millimetres. Mesh objects come too, their planes, cylinders and other simple surfaces rebuilt as true faces. Hidden objects are left out, and the result counts them.
Layers, colours, curves, annotations and Rhino history do not travel. STEP carries the geometry, which is what an engineer or machine shop needs from a designer's model.
A 3DM file is a Rhino model. Rhino is a NURBS modeller, dominant in industrial design, jewellery, marine and architecture. A 3DM can mix exact breps, surfaces, meshes and curves on layers; polysurfaces and extrusions convert exactly, and mesh objects come along: as meshes in a mesh format, rebuilt as true surfaces in a solid one.
A designer works in Rhino and engineering or manufacturing needs the shape in a format their system reads.
STEP (ISO 10303) is the closest thing engineering has to a universal solid format. It stores exact B-rep geometry — a hole is a cylindrical face, not a ring of facets. Fusion 360, Inventor, Onshape, SOLIDWORKS, Creo, NX, CATIA and FreeCAD all read it; .step and .stp are the same format. AP242 supersedes AP203 and AP214.
What you send when the other side has to keep modelling, quote machining, or open the shape in a different CAD system.
Keep the part open: fill it with a lattice, check it with FEA, texture a surface, or slice it into cut-ready sheets. These workspaces are in early access — create an account, then apply from inside the app.
Going the other way? Convert STEP to 3DM.
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