STL to OBJ Converter
Convert an STL mesh to Wavefront OBJ.
File
Result
Your converted file will appear here.
About the STL to OBJ converter
STL is a printing format: a loose bag of triangles with no shared structure. OBJ is a modelling format, which is why moving a mesh into Blender or a texturing tool usually means converting it first.
Drop an STL in and get an OBJ back, without uploading a model you may not want on someone else’s server.
Vertices are welded, not copied
STL repeats every vertex for every triangle that touches it, so a cube stores 36 vertices for its 8 corners. A straight conversion carries that waste across and gives you a mesh that cannot be smoothed or edited sensibly.
Identical vertices are merged into a shared list, which is what makes the OBJ smaller and gives the modelling package a surface it can actually work with rather than disconnected faces.
What does not survive
STL carries no colour, no texture coordinates and no materials, so none appear in the OBJ — there is nothing to carry. No .mtl file is produced, because there would be nothing in it.
Per-face normals are dropped too. They are recomputed from the winding by anything that needs them, and STL normals are frequently wrong or zero anyway.
Frequently asked questions
Can it convert OBJ back to STL?
Not yet. OBJ can contain quads, n-gons, curves and multiple objects, all of which need triangulating and flattening first — a bigger job than reading STL, and easy to do badly.
Why is the OBJ bigger than the STL?
Because binary STL stores coordinates as four-byte floats and OBJ writes them as text. Against a text STL the OBJ will be smaller; against a binary one, larger but far better structured.
Is my model uploaded?
No. The STL is parsed in your browser, which matters when the file is a client’s part or something you have not published yet. It also means a 200 MB mesh is read at disk speed rather than upload speed.