Free Online 3D File Converter

Four conversions we measured today

Both inputs were built from scratch for the test. The first is a machined-style STEP solid from FreeCAD: a plate 40 by 20 by 10 mm with a 6 mm through hole and 2 mm fillets on the vertical edges, 11 exact faces, 35 KB. The second is a Blender scene exported as GLB: a red cube and a blue sphere, 972 triangles together, with a 40-frame rotation keyed on the cube only, 74 KB.

Each file was converted twice. All four results were ready about two seconds after upload, and every mesh output had exactly the same triangle count as its source — the geometry itself is not what gets lost.

Why CAD files and mesh files behave differently

STEP, IGES, 3DM and BREP store a part as exact mathematical surfaces. STL, OBJ, PLY, GLB and FBX store it as a bag of triangles. Every CAD-to-mesh conversion crosses that line, and it only goes one way.

The test bracket shows the price exactly: a solid with 11 faces came back as 232 triangles. That is close enough to print or render, but the hole wall is now a ring of flat strips, and nothing in the file remembers it used to be a cylinder. This is also why there is no route back: STL, OBJ and PLY have no STEP target in our list, because rebuilding parametric surfaces from triangles is reverse engineering, not file conversion.

So if anyone downstream still has to edit the part, hand over the STEP or IGES original and convert to a mesh only at the end of the chain, for printing or rendering.

Units and scale, the mistake that costs the most time

STL stores bare numbers with no unit at all. Our STEP bracket arrived as 40 by 20 by 10, exactly the millimetre figures we started from, so a slicer reads it correctly. Blender, whose scene unit is the metre, reads that same file as a 40 metre plate unless you change the import scale.

The reverse hurts more. The GLB scene was authored in metres, as glTF expects, so the cube is 0.04 units across. Converted to STL, those numbers come over unchanged and a slicer sees a 0.04 mm speck instead of a 40 mm cube. When a converted print file turns out microscopic, scale it by 1000 — converting it again will not change anything.

• STL, OBJ and PLY store no unit. Whoever opens the file decides what the numbers mean.
• glTF and GLB are metres by specification, which is why web models often look tiny in a slicer.
• STEP and IGES carry their unit inside the file, usually millimetres.
• 3MF is millimetres unless the file says otherwise, which is one reason slicers prefer it to STL.
• In our test the FBX came back at exactly the size of the source GLB, so that hand-off needed no rescaling.

Choosing the output format

• STL — the safe input for any slicer and most printing services. Triangles only: no colour, no units, no separate objects.
• 3MF — the modern printing alternative, with colour, several materials and separate objects in one file. We can write it from STL and AMF.
• GLB and glTF — the default for web and real-time work. GLB packs geometry, materials, textures and animation into a single binary file.
• FBX — the usual hand-off into game engines and animation tools, and the one output in today's test that kept both materials and animation.
• USDZ — the Apple AR route, opened directly by Quick Look on iPhone and iPad. Reachable from OBJ, FBX, GLB, glTF and USD.
• OBJ — plain text and read by almost everything, but materials live in a separate MTL file, so colour is the thing that gets left behind.
• PLY — the scanning and photogrammetry format, with colour stored per vertex.
• STEP and IGES — the only outputs that keep real CAD geometry. They stay inside the CAD world: we convert IGES to STEP and STEP to IGES.
• DXF and DWG — drawing exchange for CAD. These two convert into each other and nothing else.

Point clouds, buildings and other special cases

• Scanner formats PTS, XYZ, PCD and E57 convert to PLY and nothing else. PLY is the one target that stores a cloud faithfully, colour per point included. Turning a cloud into STL or OBJ would mean meshing it, which is a modelling decision rather than a conversion.
• IFC building models convert to OBJ, FBX and DAE. The geometry survives and the building data does not: a wall arrives as a shape, not as a wall with properties. Keep the IFC if anyone needs those properties.
• OpenVDB holds a voxel volume with no surface in it, so there is nothing to convert until you mesh it in the tool that made it.
• DWG and DXF are drawings. A 2D drawing cannot become a 3D model here, and no amount of converting will add the third dimension.
• Blender project files convert to OBJ, FBX, GLB and STL, but a blend file holds far more than geometry. Anything that is not geometry or a basic material will not come across.

Limits, and what happens to your file

• Free: files up to 30 MB, 10 conversions per hour, 2 running at the same time, no account needed.
• Pro: files up to 1 GB, 50 conversions per hour, 5 at the same time, for 9.99 US dollars a month or 95.88 a year.
• Uploaded and converted files are deleted from the server within one hour of upload.
• The 3D viewer and the compressor upload nothing at all. They run inside your browser on GLB, glTF, OBJ and STL files, and the compressor always writes an optimised GLB.
• A file in a format we cannot read is stopped in the page before the upload even starts, together with the export route that does work.

Doing the same job without uploading

If a model is confidential or larger than the free limit, do it locally. Both sample files for today's test were built this way, so these are tools we actually use.

Blender reads and writes OBJ, STL, PLY, FBX, glTF, GLB, USD and Alembic through File and then Export. Apply your modifiers first, because the exported mesh is what the modifiers produce, not what the viewport suggests.

FreeCAD builds and exports STEP, IGES, BREP, STL, OBJ and DXF: select the object in the model tree, then File and Export, then pick the format. When a curved part goes out as a mesh, look for the tessellation or deviation setting — a smaller deviation means more triangles and smoother curves, and it is the single number that decides whether your fillets look round.

A slicer can stand in for a converter too: PrusaSlicer loads a model and exports the plate again as STL, which is often the shortest path from a printing file to a plain mesh.