Does the OBJ have a UV layer?

No. STL stores no texture coordinates, and nothing is invented for them, so the .obj has no vt lines. You will need to unwrap it in a 3D application before you can texture it.

Where did the colour in the .mtl come from?

Not from your file. STL carries no material data, so the material in the .mtl is the placeholder the STL reader attaches when it loads the geometry — a flat lime green (#B8FF3B) named stl_material_0. Treat it as a stand-in to replace, not a recovered colour.

Why is the download a ZIP for such a simple file?

Because an .mtl is always written for a named material, and the STL reader names its placeholder material. An .obj plus a material file has to stay in one folder, so the two are packaged together.

Is OBJ really better than STL for this?

Not inherently. STL is smaller and simpler. OBJ is worth it when the next tool only reads OBJ, or when you want a text-based mesh you can edit.

STL to OBJ Converter

Convert an STL to Wavefront OBJ, carrying the file's facet normals across for tools that only read OBJ. Runs in your browser.

Drag & drop your STL file here

or click to browse

Supported Formats

.glb.gltf.obj.fbx.stl.ply.3mf.off.zip

Format Information

Source Format

STL.stl

STL (Stereolithography)

STL is an additive-manufacturing format from the 1990s: a flat list of triangles and nothing else. It has no concept of a scene, a material or a texture, which is why it is the lingua franca of 3D printing and also its most lossy interchange format.

What it carries: Triangle positions and, optionally, one facet normal per triangle. No UVs, no vertex colours, no materials, no node hierarchy, no animation.

Open a STL file in the viewer

Target Format

OBJ.obj

OBJ (Wavefront)

The Wavefront OBJ format is a plain-text mesh description that has been the default interchange format for computer graphics since the 1990s. Geometry lives in the .obj file; colour and texture references live in a companion .mtl file.

What it carries: Vertex positions, normals, texture coordinates and polygon faces, plus what MTL can express: a diffuse colour, opacity, shininess and a single diffuse texture map. There are no PBR metal/roughness values, no normal maps, no vertex colours and no animation.

Open a OBJ file in the viewer

About this conversion

Adding a layer of structure to a bare triangle list. The STL is written as an .obj with the file's facet normals carried across as vertex normals and a placeholder .mtl alongside it, so the result is a normal-bearing mesh rather than a bare point cloud of faces.

Why convert STL to OBJ

Open an STL in software that reads OBJ but not STL — many older CAD and sculpting tools.
Get a text-based mesh you can inspect, edit or diff in version control.
Hand the shape to a tool that expects a .obj even for an untextured model.

What happens during the conversion

Geometry

The triangles are written through with the STL's facet normals carried across as vertex normals, and all geometry sits in a single object, since STL has no hierarchy. There are no texture coordinates to carry across, because STL does not store any, so the .obj has no vt lines.

Materials and textures

Nothing is carried across from the STL, because the format has no material data. What you do get is the fixed material the STL reader attaches on load — a lime green (#B8FF3B) standard material — written out as an .mtl entry named stl_material_0, with a diffuse colour and no texture map.

Common use cases

Opening a print file in an OBJ-only tool.
Producing an inspectable text mesh for review.
Submitting a shape to a service that accepts OBJ but not STL.

Limitations of this conversion

The colour in the .mtl is not yours. It is the placeholder the STL reader attaches — a flat lime green (#B8FF3B) — not a colour recovered from your file, so expect to reassign it.
There are no UVs, because STL has none. Any texture layout will have to be created from scratch.
Single merged object: the STL's lack of hierarchy means none can be recovered.
Because the .mtl is present, the download is a ZIP rather than a bare .obj. Keep the .obj and .mtl in the same folder.

How to convert STL to OBJ

Three steps in the browser. Nothing is uploaded to a server, so an unwieldy file is limited only by your own device's memory.

STEP 1

Upload your .stl

Binary and ASCII STL are both supported, and each facet normal is carried over to the three vertices of its triangle.

STEP 2

Convert to OBJ

Triangles are written with the STL's facet normals carried across as vertex normals, alongside a small .mtl.

STEP 3

Unpack and open the .obj

Keep the .obj and .mtl together. Expect a single object with no UV layer and a placeholder lime-green material.