How to convert OBJ to STL
- Drop your .obj file into the box above, or click Choose file.
- Check the 3D preview, size and triangle count.
- Make sure STL is selected as the output format. Adjust scale or up-axis if needed.
- Click Download. The .stl file is created instantly on your device.
Why convert OBJ to STL?
Slicers want STL. Converting OBJ to STL drops materials and UV coordinates and keeps the surface triangles, which is exactly what a 3D printer needs. Quads and n-gons in the OBJ are split into triangles automatically.
What changes in the conversion
- Textures are dropped. STL cannot store image textures.
- Units. STL is defined in metres. Large models (in millimetres) are scaled ×0.001 automatically so they appear at real size.
- Up-axis. OBJ is Y-up while STL is usually Z-up; the model is rotated so it stands the right way up. Untick "Convert up-axis" to keep the raw coordinates.
- Geometry is preserved. Every triangle, with all object transforms applied, ends up in the new file.
OBJ vs STL
| OBJ | STL | |
|---|---|---|
| Full name | Wavefront OBJ | Stereolithography |
| Stores | geometry, normals and UV coordinates (materials live in a separate .mtl file) | geometry only |
| Colour | No | No |
| Textures | Yes | No |
| Units | none | none – most programs read STL numbers as millimetres |
| Exact CAD geometry | No | No |
About the formats
OBJ (Wavefront OBJ) was introduced by Wavefront Technologies for its Advanced Visualizer software. It is a plain-text mesh format that stores vertices, faces, normals and texture coordinates, with materials in a separate MTL file. It is widely used to move models between 3D modelling programs such as Blender, Maya, 3ds Max and ZBrush.
STL (Stereolithography) was created by 3D Systems in 1987 for its stereolithography printers. It describes only the surface of a model as a list of triangles, without colour, materials or units. It is the default file for 3D printing and the format almost every slicer (Cura, PrusaSlicer, Bambu Studio, Chitubox) opens.
Frequently asked questions
Is this converter free?
Yes. You can convert OBJ to STL for free – up to 3 conversions a day, with no sign-up and no watermark. If you need more, Pro gives you unlimited conversions and batch conversion (free for 7 days).
Are my files uploaded to a server?
No. The conversion runs entirely in your browser using WebAssembly and JavaScript. Your model never leaves your computer, which also makes it safe for confidential parts and patient data.
Is there a file size limit?
There is no fixed limit. Files of a few hundred megabytes work on a typical laptop; the practical limit is your device's memory.
What happens to the textures and the .mtl file?
STL cannot store colour or textures, so they are left out. The shape is kept exactly. If you need colour for multi-material printing, convert to 3MF instead.