Why convert OBJ to STL
OBJ is common for models made in Blender, Maya, ZBrush and game pipelines, and for downloads from 3D asset sites. Slicers read OBJ more and more, but STL remains the format every printer workflow, print service and repair tool accepts without question.
The unit question
OBJ stores bare numbers. A character modelled in centimetres or a scene in metres opens in a slicer as a tiny speck, because the slicer assumes millimetres. Before converting, set The file is in to the unit the OBJ was made in:
| Source tool or site | Usual unit |
|---|---|
| CAD exports, most printables | Millimetres |
| Maya, 3ds Max, many game assets | Centimetres |
| Blender default scenes, photogrammetry | Metres |
| US-based CAD set to imperial | Inches |
The summary shows the resulting size in millimetres before you download, so you can check that a mug is 90 mm tall rather than 0.09 or 9,000.
What is kept and what is dropped
- Geometry: every face, triangulated where it had four or more corners.
- Groups and objects: merged into one mesh in place.
- Materials: STL has none. 3MF output keeps the solid
Kdcolours from the.mtl. - Textures, UVs, normals and smoothing groups: not used for printing and not written.
Before you print
Models made for rendering are often not solid: separate floating parts, open edges, intersecting shells. The converter's summary tells you whether the mesh is watertight. If it is not, the slicer may still cope; if it does not, see watertight and manifold meshes.
On a phone
OBJ conversion works in a phone browser. The Mes3D app for iPhone, iPad, Mac and Android opens OBJ files from Files or Mail, lets you fix the unit or resize to exact dimensions, and exports STL, OBJ or 3MF.