STL file format
The plain triangle format that every slicer and CAD program reads. It describes a surface and nothing else.
Runs locally — your files never leave your device
Tools for STL
Each one runs in your browser; your files are never sent anywhere.
What is STL?
STL was created by 3D Systems in 1987 for its stereolithography printers. A file is a list of triangles; each triangle stores a normal and its own three corners, so corners shared by neighbouring triangles are written again for every triangle.
There are two encodings. Binary STL has an 80-byte header, a 4-byte triangle count and 50 bytes per triangle. ASCII STL writes the same data as text between "solid" and "endsolid" lines and is several times larger.
STL stores no units, no colours, no materials and no names of parts. Slicers read the numbers as millimetres.
STL at a glance
| Property | STL |
|---|---|
| Full name | Stereolithography (also read as Standard Triangle Language) |
| Extension | .stl |
| MIME type | model/stl |
| Encoding | Binary or text (ASCII) |
| Surface | Triangles only |
| Shared vertices | No, every triangle stores its own corners |
| Colours and materials | No, not in the standard |
| Units | Not stored |
| Several objects | No, one list of triangles |
| Opened by | Every slicer and CAD program |