OBJ to STL Converter
Convert an OBJ file to an STL you can slice. OBJ has no units, so choose them here, stand the model the right way up, see if it is watertight, and download a checked STL.
- 1Drop the file
- 2Check it
- 3Download STL
1Drop your OBJ file
Drop a .obj file here, or choose one. It stays on your device.
Working…
This browser can't show the 3D view (WebGL is off). The check and the download still work.
Turns on when the STL has been read back and is watertight. Binary STL, millimetres.
Your file is read by this browser tab. Nothing is uploaded, and the STL is saved straight from this page.
2About this file
- Kept: vertices and faces. Quads and larger polygons are split into triangles.
- Ignored: the .mtl file, textures, normals and UVs. There is no need to add them.
- Not read: curves and free-form surfaces.
3Size and direction
How to convert OBJ to STL
- Drop the OBJ. You don’t need its .mtl file or textures, as STL can’t use them.
- Choose the units. An OBJ only holds numbers. If the size looks 10 or 25.4 times off, the file was drawn in centimetres or inches, so change File units.
- Stand it up. Blender, Maya and many other programs export OBJ with Y up. Printers use Z up. Switch the Up axis to Y if the model lies on its back.
- Read the check, then download. The button turns on when the STL passes.
Units and Y-up in OBJ files
OBJ doesn’t say which unit its numbers are in or which way is up. The program that opens it has to guess. Slicers read an STL’s numbers as millimetres, so getting this right here saves a surprise later. The size shown above the check is the size in the file you download.
Quads and polygons become triangles
STL only stores triangles, so a four-sided or larger face in your OBJ is split into triangles across its corners, including faces with an inward corner such as an L shape. On a flat face you won’t see any change. A strongly bent polygon may look different, because the file never said what its surface did between the corners.
What the check proves
The download button starts off. The page writes the STL, reads those bytes back the way another program would, joins corners that match to 0.0001 mm, and only turns the button on if every edge joins exactly two faces and the size matches. If it doesn't pass, you see how many open and non-manifold edges there are, and you can run the simple repair. The repair closes holes and turns faces, and it can change the shape, so it only runs if you press it. Some files can't be fixed this way, and those need Blender or MeshLab. The check is about the file, not about how it will print.
FAQ
How do I convert OBJ to STL?
Drop the OBJ here, choose the units, read the check and press Download STL. It takes a few seconds for most files, there is no account, and the file stays on your device.
Do I need the MTL file?
No. The .mtl file and textures describe colours and surfaces, and STL can’t store those. The shape is all in the .obj.
Is STL or OBJ better for 3D printing?
Both describe a surface. STL is the plain choice and every slicer reads it. OBJ can also carry colours through its materials, but slicers often ignore them. Neither stores units, so check the size.
Why is my OBJ lying on its side after converting?
Many programs export OBJ with Y as the up axis. Set the Up axis to Y on this page, or use the 90° turn buttons, and the STL is written that way.
Why does my OBJ say it isn’t watertight?
Models made for animation or games are often open shells or separate overlapping pieces. They look solid but have no closed inside. The check counts the open edges. Try the simple repair, or fix it in Blender or MeshLab.