How do I open an STL file on Windows?

Right-click and open with the built-in 3D Viewer to look at it. To print it, load it into a slicer such as PrusaSlicer or Cura. To edit the mesh, use Blender.

What is the difference between STL and STEP?

STL is a triangle mesh of the surface, which is what printers need but which cannot be edited as engineering geometry. STEP holds exact solid geometry you can modify and measure. Keep the STEP as the master and export STL for printing.

File extensions

How to open a .stl file

Stereolithography mesh · 3D / printing

An .stl file is a 3D model made of triangles, the standard for 3D printing. Windows 10 and 11 display one in the built-in 3D Viewer, and Blender or FreeCAD open it for editing.

What a .stl file actually is

STL describes only the surface of an object as a mesh of triangles. No colour, no materials, no units, no internal structure. That minimalism is exactly why every 3D printer accepts it.

The trade-off is that a mesh is not CAD. You cannot change a dimension in an STL the way you can in a STEP file, because the original geometry has already been approximated away.

Why it will not open

On Windows the 3D Viewer handles STL but is not associated with the extension by default, so a double-click asks what to use. macOS has no built-in viewer at all.

Step by step

Windows

01To look at it: right-click, choose "Open with", then 3D Viewer.
02To prepare it for printing: load it in your slicer, such as PrusaSlicer, Cura or Bambu Studio. That is where scaling, orientation and supports happen.
03To edit the mesh: Blender is free and handles STL well.
04To repair a broken mesh, most slicers now fix minor errors automatically and will tell you when they have.

macOS

01Install Blender or FreeCAD, or "brew install --cask blender".
02Preview does not open STL.

What usually goes wrong

STL carries no units

The file stores numbers with no statement of whether they mean millimetres or inches. A model that arrives at 1/25th of the expected size was authored in inches and read as millimetres. Slicers let you scale by 25.4 to correct it.

Why there is no download list here

We index 177 programs and none of them opens .stl files, so there is nothing for us to publish a verified download for. The software named in the steps above is the right answer for this format; we simply do not have its installer on record yet.

Common questions

How do I open an STL file on Windows?: Right-click and open with the built-in 3D Viewer to look at it. To print it, load it into a slicer such as PrusaSlicer or Cura. To edit the mesh, use Blender.
What is the difference between STL and STEP?: STL is a triangle mesh of the surface, which is what printers need but which cannot be edited as engineering geometry. STEP holds exact solid geometry you can modify and measure. Keep the STEP as the master and export STL for printing.