OBJ to STL Converter

OBJ is a common exchange format for 3D graphics: it stores vertices and faces, and optionally normals, texture coordinates and a reference to a material file. Slicers want something simpler. STL holds only triangles, and almost every slicer and CAD program opens it. Converting OBJ to STL keeps the shape and drops everything else, which is exactly what a printer needs.

Only the geometry is read from the OBJ. The .mtl file with colors and the texture images are ignored, because STL cannot store them. If you need a colored print, keep your OBJ for your slicer's paint tools or a multi-material workflow and use the STL only for single-color printing.

If the OBJ contains quads or larger polygons, they are split into triangles in the STL, which is what STL requires. The shape does not change.

The most common surprise with an OBJ is size. Blender and many modeling tools work in meters or arbitrary units, so a model that looks 1 unit wide may arrive as 1 mm in your slicer. Use the "Units in the file" selector: if the OBJ was exported in meters pick m, and the STL is written in millimeters at the right size. Always check the size shown next to the preview before you download.

The tool also rotates models between up-axis conventions when you convert between formats that disagree. OBJ itself has no fixed up axis, so if your model lies on its back, rotate it in your slicer.

A converter cannot fix a broken model. Holes, flipped faces and loose triangles in the OBJ will still be there in the STL, and your slicer may warn about non-manifold edges. For scans and sculpts, run a mesh repair in your slicer or modeling tool after converting. Very large OBJ files, such as high-resolution scans, depend on your device's memory and may be slow on a phone.