Online OBJ to STL Converter
Drop an OBJ file to check it in 3D and download it as STL, ready for 3D printing. Everything runs in your browser: nothing is uploaded.
How to convert OBJ to STL
- 1
Drag your OBJ file onto the box above, or click it to choose a file.
- 2
Check the size in the measurements panel: OBJ files have no units, so millimeters are assumed.
- 3
Rotate the model 90° if it should sit on another face of the print bed.
- 4
Click “Download STL” and open it in your slicer.
What changes in the conversion
OBJ files can have faces with four or more sides: the converter splits them into triangles, which is what STL and slicers need. Materials and textures (.mtl files) are not used, because STL only stores geometry.
OBJ models are usually built with Y up, while 3D printing uses Z up. The converter turns the model so it stands upright on the bed.
Before printing
Models made for games or animation are often open surfaces or have very thin walls. If the slicer complains, check that the mesh is closed and that the walls are thick enough for your nozzle.
Frequently asked questions
Is the OBJ to STL converter free?
Yes. You can convert files for free, without an account and without watermarks.
Are my files uploaded to a server?
No. The OBJ is read and converted entirely in your browser and never leaves your device.
What size will the STL be?
OBJ files do not store units, so the values are taken as millimeters. If the model looks too small or too large, scale it in your slicer.
Do I need the .mtl file?
No. The .mtl file only describes colors and textures, which STL cannot store. Just drop the .obj file.
Can it convert large OBJ files?
Yes. Files are read in the background so the page stays responsive. The limit depends on the memory of your device.