Why convert STL to OBJ
STL is a printing format: a flat list of triangles where every corner is written again for every triangle that touches it. OBJ is a modelling and interchange format with a proper vertex list. Game engines, renderers and older 3D tools often prefer OBJ, and a welded vertex list is the starting point for smoothing, UV unwrapping or retopology.
What the converter does
- Reads the STL (binary or ASCII).
- Welds identical corner positions into one shared vertex, so the OBJ stores each point once and faces refer to it by index.
- Writes
vandflines in millimetres — or scaled from the unit you choose, if the STL was exported in inches, centimetres or metres.
The geometry is unchanged: the same triangles, in the same place.
STL vs OBJ at a glance
| STL | OBJ | |
|---|---|---|
| Vertex sharing | No — corners repeated | Yes — indexed |
| Polygons | Triangles only | Triangles, quads, n-gons |
| Materials and UVs | No | Yes (via .mtl, not written here) |
| Typical use | 3D printing | Modelling, rendering, games |
A note on smoothing
STL meshes from CAD are faceted on purpose. After importing the OBJ into a modelling tool, use flat shading for hard-edged parts, or "shade smooth by angle" for organic ones — the welded vertices make that possible.
On a phone
STL to OBJ conversion works in a phone browser. The Mes3D app for iPhone, iPad, Mac and Android exports OBJ, STL or 3MF directly after resizing or cutting a model.