STLPalGuides / Updated October 10, 2026
What is an STL file?
An STL file is a 3D shape made of triangles. It's the file most 3D printers and slicers expect, because it holds the shape and nothing else.
What's inside
An STL is a long list of triangles. Each triangle has three corner points and a direction it faces. Put enough of them together and you get any shape: a cube needs 12, a detailed figure can need millions.
That's all there is. No colour, no material, no unit and no print settings.
Where it came from
3D Systems created STL in 1987 for its stereolithography printers, which is where the name comes from. It was simple enough that every tool learned to read it, and it's still the default today.
The two kinds of STL
| Binary STL | Text (ASCII) STL | |
|---|---|---|
| How it's stored | Packed numbers | Readable text, one line per value |
| Size | 50 bytes per triangle | Several times bigger |
| Common? | Yes, the usual kind | Mostly from older tools |
Both hold the same shape. A million-triangle model is about 50 MB as binary STL.
Why STL causes trouble
- No unit. Slicers assume millimetres. A model made in metres or inches comes in far too small. Fix it with a resize, like our STL editor's Inches → mm button.
- No colour. Colour has to come from your filament or from painting in the slicer.
- No sharing between triangles. Each one repeats its own corners, so the files are big and small gaps are easy to create.
How to open and make one
- Open: any slicer (Bambu Studio, PrusaSlicer, OrcaSlicer, Cura), Blender, or our free STL viewer in the browser.
- Make: export from a CAD app such as Tinkercad, Fusion or Onshape, or from Blender with File → Export → STL.
- Download: MakerWorld, Printables and Thingiverse all have STL files.