Convert STL to OBJ

What converting STL to OBJ does

STL stores every triangle on its own, so each corner point is written again for every triangle that touches it. OBJ is the Wavefront format that almost every 3D app reads. It lists each vertex once and builds faces by pointing at those vertices. The converter reads the STL triangles, merges corners that sit at the same position, writes one normal per face and saves an indexed OBJ mesh.

Why convert STL to OBJ?

Many 3D editors, game engines, AR viewers and rendering tools import OBJ more readily than STL. Because shared vertices are merged, the OBJ is a connected mesh, so smoothing, UV unwrapping and sculpting tools treat it as one surface instead of loose triangles. OBJ is also plain text, so you can inspect or edit it in any text editor.

How to convert STL to OBJ

Drop one or more .stl files above and press Convert all. Binary and ASCII STL are both detected automatically. Each file becomes a .obj with the same name, which you can download on its own or with the rest in a ZIP. Coordinates stay in the units of the original file, which for 3D printing models is almost always millimetres. To look at a model before converting it, open it in the STL viewer.

What the OBJ contains

The OBJ holds the geometry only: vertices, face normals and triangular faces. STL has no colors, textures or UV coordinates, so there is nothing to put in a material (.mtl) file. Degenerate triangles with zero area are left out. Coordinates are written with seven significant digits, the same precision STL stores.

Before you start

Input: STL. Output: OBJ. The settings appear before anything runs, so you can check them first. Your original file is never changed.

These formats often follow rules set by one app or device. Test the result where it will be used, and keep the source in case you need to export it again.

Keep the original until you have opened and checked the result. The work happens in this browser tab, so the size you can handle depends on your device's memory, your browser and the file itself.

Steps to convert STL to OBJ

1. Drop your .stl files into the box above, or browse to pick them.
2. Press Convert all. The conversion runs in your browser.
3. Download each OBJ, or all of them as a ZIP.
4. Import the OBJ into Blender, a game engine or any 3D app.