What carries over from 3MF to OBJ
3MF belongs to the printing world. Rendering, animation and sculpting programs read OBJ far more often. If you want to pose a printed figurine in a scene, sculpt extra detail on it or texture it, OBJ is the hand-off format.
| Item | 3MF | OBJ |
|---|---|---|
| Mesh | triangles | the same triangles |
| Unit | in the package | not stored; numbers are millimetre values |
| File type | package | plain text |
Our round-trip test saved a 20 mm cube as OBJ and re-opened it with the same size, volume and triangle count.
Scale in the target program
OBJ numbers stay in millimetres, but a 3D program may read them as metres or centimetres. A 20 mm part can then import as 20 m. Set the import unit to millimetres, or scale the object down after import, and the model takes its real size. A program that works Y-up may also show the part lying on its back, so turn it 90 degrees there.
From 3MF file to OBJ file
- Drag the .3mf onto the tool or press Open File.
- Check the size and part count in Info.
- Press Download OBJ.
- Import the OBJ in your 3D program and set its scale.
Unzipping the package and writing the OBJ both happen in this tab, so the model does not travel over the network.
What the OBJ file looks like inside
Open the downloaded OBJ in a text editor and you will see why it travels so well between programs. Each line starting with v holds one vertex as three numbers, and each line starting with f lists the vertices of one face. The 3MF package with its XML model and unit attribute is gone. What remains is a list any 3D program can parse, with millimetre values that carry no label.
Fixing common import problems
If the part imports a thousand times too large, the program read millimetre values as metres, and 20 mm became 20 m. Scale by 0.001 or set the importer to millimetres. If the part spins around a point far away, its origin sits off the model; press Center on origin before you download.
A print mesh has hard edges between flat triangles, so it can look faceted in a render. Most 3D programs can smooth the shading without adding triangles. If sculpting reveals small holes or loose shells, run Repair mesh here first; it reports what it closed.
Lighten the mesh for real-time tools
Print models are often far denser than a game engine or a web scene needs. Edit → Reduce triangles takes the count down to a percentage you choose before the OBJ is written. In our test a sphere cut to 30 % of its triangles kept its volume within 2 %, so the silhouette stays the same while the file shrinks. Undo brings back the full mesh if the result looks too rough.
Two more edits help before export. Center on origin puts the pivot in the middle of the part, and Rotate sets the axis your program expects.
Look inside before you hand it on
A 3MF made for printing may hide internal walls or overlapping bodies that only matter once you render or sculpt. The section plane cuts through the model along X, Y or Z and shows the inside in red. Info counts separate parts, so a figure that should be one piece but reads 3 parts tells you the mesh has loose shells.
Other routes out of a 3MF
For a slicer or a model site, 3MF to STL gives the standard print mesh. For CAD, 3MF to STEP writes a faceted solid. The way back after editing is OBJ to 3MF. The 3MF viewer and OBJ viewer let you inspect either file without converting.
Questions and answers
Is the OBJ the same size as the 3MF?
The numbers are the same millimetre values. OBJ has no unit field, so the receiving program decides how to read them; set its import scale.
Can I edit the mesh before converting?
Yes. Edit in the viewer can scale, rotate, cut, repair or reduce triangles; the OBJ saves the edited state.
Is the 3MF sent to a server for conversion?
No. The 3MF is unpacked and the OBJ is written by JavaScript in your tab, and the file stays on your device.
Does the converter work on a phone?
The layout was tested at 390 px width without sideways scrolling. Heavy models need memory, so a desktop browser is the safer choice for big files.
Why does the OBJ come in a thousand times too big?
The target program treats the numbers as metres. The file holds millimetre values, so set the import unit to millimetres or scale the object by 0.001.
Which programs can open the OBJ?
Most rendering, sculpting and game tools import OBJ. If yours reads glTF better, convert the OBJ again with OBJ to GLB.