Why is my converted STL grey when the GLB was coloured?

STL has nowhere to put a colour. It stores triangles only, so every STL is grey until a program paints it. To keep colours, convert to GLB or glTF instead.

Can I convert several models at once?

One at a time here. Each conversion is a few seconds, and a GLB with several meshes comes out as one file in every format.

3D Model Converter

Convert between OBJ, STL, GLB and glTF in your browser. Drop a model, check it in the viewer, and download it in the format you need. Nothing is uploaded.

Drop a 3D model

OBJ, STL, GLB or a self-contained glTF, up to 150 MB.

About this tool

Converts a 3D model between the four formats that cover most of the ground: OBJ, STL, GLB and glTF. Drop the file, look it over in the viewer, and download it as any of the others. An OBJ from a modelling program becomes the STL a slicer wants; a GLB from a scanner or a game asset becomes an STL or an OBJ for CAD; an STL becomes a GLB for a web page. The file is read and written with three.js in your browser, so a fifty-megabyte scan never leaves your computer.

How to use it

1Drop an OBJ, STL, GLB or glTF. The viewer shows it, with the triangle count and the size in the file's own units.
2Turn it around to check it is the right model, and switch on wireframe to see the mesh.
3Press the format you need. The file downloads, and the Send to menu can pass it to the viewer or the STL tools.

Good to know

What each format keeps

STL is triangles and nothing else, which is why every slicer and CAD program reads it and why a coloured model comes out grey. OBJ keeps the mesh and names its materials in a sidecar file this tool does not write. GLB and glTF keep materials, colours and textures, in one binary file or as readable JSON with the buffers embedded. Converting a GLB to STL therefore loses the look and keeps the shape; the other way, an STL gets a neutral grey material. The file is read into memory by your own browser and processed there, so it is never uploaded and never reaches a server.

glTF files that refer to other files

A .gltf often points at a .bin buffer and image textures beside it. A single dropped file cannot reach those, so the tool asks for a .glb or a glTF exported with everything embedded. Draco and meshopt compression and KTX2 textures are not decoded yet either; export without them.

Units and scale

None of these formats records a unit. The numbers are copied through as they are, so a model drawn in millimetres stays in millimetres. If your slicer opens the STL at a tenth of the size, the source was in centimetres; scale it there.