Di Huy Nguyen · ·
A STEP file holds a part as exact mathematical surfaces. An FBX file holds triangles, plus the scene extras that game engines and animation tools expect. Converting STEP to FBX is the moment a CAD part stops being CAD, and it is a one-way door, so it is worth knowing exactly what comes out the other side.
People need this hand-off for a handful of jobs: dropping a mechanical part into a game engine, building a product animation or turntable render, feeding a real-time configurator, or giving a modelling artist something to work with. All of those only need the shape, which is why the conversion suits them and is wrong for anyone who still has to edit the part.
Today we built two STEP files from scratch, converted both to FBX through the same pipeline this page uses, then opened the results in Blender 5.1 and also read the raw numbers straight out of the FBX files. Everything below comes from those measurements.
What the two test conversions kept and lost
The first input was a single machined part: a plate 40 by 20 by 10 mm with a 6 mm through hole and 2 mm fillets on its four vertical edges, 11 exact faces, 35 KB. The second was an assembly stored in one STEP file: a 60 by 40 by 8 mm base plate with an 8 mm hole, plus a separate pin 7.8 mm across and 25 mm tall, 23 KB. Both results were ready in about two seconds.
| Conversion | Result | Kept | Lost |
|---|---|---|---|
| Single part to FBX | 15.4 KB binary FBX, 232 triangles | The whole shape, the hole, the 2 mm fillets, and the millimetre figures 40 by 20 by 10 | The exact curved surfaces, any way back to editable CAD, and the part name from the STEP file |
| Two-solid assembly to FBX | 15.1 KB binary FBX, 220 triangles | Both bodies, correctly positioned relative to each other | The split between the two bodies: they arrive welded into a single mesh object |
An assembly comes back as one mesh
This is the finding most likely to cost you time. Our second STEP file contained two clearly separate solids. The FBX contained one mesh object of 220 triangles, with the base plate and the pin merged into it. You cannot select the pin on its own, move it, or give it its own material without cutting it out of the mesh by hand.
If the bodies have to stay apart, export them as separate STEP files from your CAD program and convert them one at a time. That takes a minute and saves an hour of mesh surgery. The same logic applies to materials: a single mesh can only sensibly carry one material, so the split has to exist before you start shading anything.
The FBX is Y-up, and Blender will not turn it over for you
CAD works Z-up. FBX works Y-up. Our converted files follow the FBX convention correctly: reading the vertex array straight out of the file, the 40 by 20 by 10 mm plate measures 40 along X, 10 along Y and 20 along Z, and the header declares Y as the up axis. That is exactly what a Y-up tool expects.
Blender is the case you will actually notice. Imported into Blender 5.1 with default settings, the same plate measures 40 by 10 by 20 and lies on its side, because the importer leaves the axes as it finds them. Either tick Manual Orientation in the FBX import panel and set Up to Y, or rotate the object 90 degrees about X after import. Fix it once, at import, rather than per object.
Units: the numbers survive, their meaning does not
STEP files normally carry millimetres, and this conversion passes the numbers through untouched. Our 40 mm plate is 40 units wide in the FBX, and the unit scale factor in the file is left at 1. Nothing is rescaled for you.
So whether the part arrives at a sensible size depends entirely on what one unit means in the program you open it in. A 40 mm bracket that shows up 40 metres wide is a unit mismatch, not a broken conversion: scale by 0.001 for a metre-based scene, or by 0.1 for a centimetre-based one. Check the dimensions of the imported object before you build anything around it.
Tessellation, and why the fillets look faceted
Tessellation is the real price of this conversion. Eleven exact faces became 232 triangles, and the ten faces of the assembly became 220. The 6 mm hole is now a ring of flat strips and the 2 mm fillets are a few narrow bands. At render distance nobody notices; in a close-up hero shot they will.
There is no tessellation or quality dial on this page, so the conversion runs at one fixed density. If a curved detail matters, control the tessellation where the part lives: FreeCAD lets you set the mesh deviation when it exports a shape as a mesh, and a smaller deviation means more triangles and rounder curves. Bring that mesh into your DCC tool and write the FBX from there.
If your file ends in .stp
STP and STEP are the same format; the shorter extension is a leftover from three-character filenames. The converter reads both, and we checked it: a copy of our test part renamed to .stp produced a byte-for-byte identical FBX.
The catch is the list on this page. Once you drop a file, the target list narrows to the formats officially listed for that extension, and for .stp those are STL, OBJ and IGES. Renaming the file to .step before uploading puts FBX back in the list.
Doing the same job without uploading
- Blender cannot read STEP, so a two-step route is normal: export the part from CAD as OBJ or STL, import that into Blender, then use File, Export, FBX. You get tessellation control on the CAD side and FBX options on the Blender side.
- FreeCAD opens STEP and exports STL, OBJ, IGES, BREP and DXF. Select the object in the model tree first, then File and Export, otherwise the export has nothing to write.
- The Blender FBX exporter lets you set the forward and up axes and a scale factor, which is usually easier than rotating and scaling objects afterwards.
- Apply your modifiers before exporting, because what leaves the file is the evaluated mesh and not the viewport preview.
Limits here, and what happens to your file
- Free: up to 30 MB per file, 10 conversions per hour, 2 running at the same time, no account needed.
- Pro: up to 1 GB per file, 50 conversions per hour, 5 at the same time.
- Uploaded files and their converted results are deleted from the server within 1 hour of upload.
- Native CAD files such as SLDPRT, PRT, ASM and CATPart cannot be read at all. Export a STEP file from the program that made them first, then come back to this page.
Tested on 27 October 2026: a FreeCAD STEP part (plate 40 by 20 by 10 mm, 6 mm hole, 2 mm fillets, 35 KB) and a two-solid STEP assembly (60 by 40 by 8 mm plate plus a 25 mm pin, 23 KB), both converted to FBX here, then re-imported in Blender 5.1 and also read directly out of the FBX files to check triangle counts, object count, materials, up axis and unit scale.