Are the STL samples ASCII or binary?

The sized samples are ASCII STL, which can be padded to an exact byte count with blank lines. The curated library adds a binary STL file, a unit cube of 12 triangles.

Can the sample model be 3D printed?

The sized samples are an open, terrain-like surface with no thickness, intended for testing importers and viewers. The binary cube is a closed, watertight solid that a slicer will accept.

What is the MIME type of an STL file?

The MIME type is model/stl. You will also meet application/sla and application/vnd.ms-pki.stl in practice. The file extension is .stl.

Is a sample STL file the same as a dummy or example STL file?

Yes. Sample, test, dummy and example STL files are different names for the same thing: an STL file with known contents that stands in for a real one. Any file on this page will do wherever a tutorial or a test plan asks for a dummy STL file.

Free STL sample files

The standard file for 3D printing: a bare list of triangles, as text or as binary. Download valid STL test files in 4 exact sizes, from 1 KB to 1 MB, each with a checksum.

Extension: .stl
MIME type: model/stl
Kind: Text
Category: 3D Models

STL files by size

Every file below is a valid STL 3D model (stereolithography) file of exactly the stated size. Open a file's page for its checksum and contents, and to preview it in your browser before downloading.

STL sample files by size
File	Size	Contents	Download
1 KB STL samplesample-stl-1kb.stl	1 KB1,024 bytes	Triangles: 4	Download STL
10 KB STL samplesample-stl-10kb.stl	10 KB10,240 bytes	Triangles: 54	Download STL
100 KB STL samplesample-stl-100kb.stl	100 KB102,400 bytes	Triangles: 572	Download STL
1 MB STL samplesample-stl-1mb.stl	1 MB1,048,576 bytes	Triangles: 5,676	Download STL

More STL samples

Hand-designed files with realistic content or a specific edge case.

Curated STL sample files
File	Size	Contents	Download
Binary STL cube (12 triangles)sample-cube-binary.stl	684 B684 bytes	Triangles: 12	Download STL

What is an STL file?

STL describes the surface of an object as triangles and nothing else. Each triangle is three corner points and a normal vector that says which side faces outwards. The format was created in 1987 for the first stereolithography printers, and every slicer and CAD package still reads and writes it.

There are two encodings. ASCII STL spells each triangle out as text between "solid" and "endsolid". Binary STL has an 80-byte header, a 32-bit triangle count and exactly 50 bytes for each triangle, which makes it about a fifth of the size.

How to recognise an STL file

Software recognises an STL file by its file signature: fixed bytes at the start of the file, also called magic bytes or a magic number.

73s6Fo6Cl69i64d

The first bytes of every file. ASCII files only. A binary STL file has no signature: it begins with an 80-byte header of free text.

Extension	.stl
MIME type	model/stl
Also seen as	application/sla, application/vnd.ms-pki.stl
Origin	3D Systems, 1987
Encodings	ASCII (text) and binary
Binary layout	80-byte header, 4-byte count, 50 bytes per triangle
Not stored	Units, colour, materials and shared vertices

What to test for

These are the behaviours that most often go wrong when software handles STL files.

A binary file may start with the word "solid" in its free-text header, and many do. Detection has to test whether the file length equals 84 plus 50 bytes for each triangle, not just read the first five bytes.
STL has no unit of measurement. A model drawn in inches and read as millimetres comes out 25 times too small.
The .stl extension is also used for Windows certificate trust lists, which is why some servers label a 3D model application/vnd.ms-pki.stl.

Strengths of STL

Accepted by every slicer, CAD package and print service.
So simple that a reader or writer is a few dozen lines of code.

Limitations of STL

No units, colour or materials.
Every triangle repeats its corner points, so files are large and shared edges must be rediscovered.

Typical uses of STL test files

Testing 3D model upload for print services
Checking detection of ASCII and binary files
Verifying volume, surface-area and bounding-box calculations
Load-testing viewers with large meshes

Software that opens STL

Cura, PrusaSlicer and other slicers
Blender, FreeCAD and Fusion
MeshLab and Windows 3D Viewer
trimesh, numpy-stl and three.js

Specifications

IANA registration of model/stl

STL sample files: questions

Are the STL samples ASCII or binary?: The sized samples are ASCII STL, which can be padded to an exact byte count with blank lines. The curated library adds a binary STL file, a unit cube of 12 triangles.
Can the sample model be 3D printed?: The sized samples are an open, terrain-like surface with no thickness, intended for testing importers and viewers. The binary cube is a closed, watertight solid that a slicer will accept.
What is the MIME type of an STL file?: The MIME type is model/stl. You will also meet application/sla and application/vnd.ms-pki.stl in practice. The file extension is .stl.
Is a sample STL file the same as a dummy or example STL file?: Yes. Sample, test, dummy and example STL files are different names for the same thing: an STL file with known contents that stands in for a real one. Any file on this page will do wherever a tutorial or a test plan asks for a dummy STL file.