What is a .stl file?
Stereolithography · 3D model · 3D Systems · 1987
STL is the standard file for 3D printing. It describes an object's surface as a mesh of triangles, with no colour or texture, which is all a slicer needs to turn a model into printer instructions.
What is a .stl file used for?
An STL stores only geometry: a shell of triangles that defines the object's surface. It carries no colour, material or units, just shape.
That minimalism is exactly why it became the universal handoff format between 3D modelling software and slicers that drive 3D printers.
For prints that need colour or texture, richer formats like OBJ, 3MF or glTF are used instead.
How to open a .stl file
The .stl format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list. For a step-by-step walkthrough, see how to open a .stl file.
Windows
- Cura
- PrusaSlicer
- Windows 3D Viewer
- Blender
macOS
- Cura
- PrusaSlicer
- Blender
Linux
- Cura
- PrusaSlicer
- Blender
- MeshLab
Web
- Online STL viewers
How to convert a .stl file
You can convert a .stl file to OBJ, 3MF, GLTF using a conversion tool or the export menu of an app that opens it.
.stl file signature (magic bytes)
Programs recognise a .stl file by the bytes at the start of the file, not by its name. These are the signatures for STL.
| Hex signature | Offset | Note |
|---|---|---|
| 73 6F 6C 69 64 | 0 | 'solid' (ASCII STL) |
| (no fixed signature) | 0 | binary STL has an 80-byte header, no fixed magic |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .stl file?
STL is the standard file for 3D printing. It describes an object's surface as a mesh of triangles, with no colour or texture, which is all a slicer needs to turn a model into printer instructions.
How do I open an STL file?
Use a 3D printing slicer like Cura or PrusaSlicer, the built-in 3D Viewer on Windows, or Blender for editing.
Can STL files have colour?
No. STL stores only shape. For colour or texture, use OBJ, 3MF or glTF.
Related formats
Sources
Details on this page were checked against authoritative references: