Does it count ASCII STL?

Yes. Binary STL uses triangle-aligned streaming and ASCII STL streams line by line.

What is a degenerate triangle?

A triangle whose three vertices collapse to a line or a point. It has no area and is skipped.

Is the triangle count exact?

Yes for the emitted geometry. Degenerate triangles are reported separately.

Does the triangle count include hidden or duplicate faces?

It counts every triangle in the file, including duplicate, degenerate, and hidden geometry. Two coincident faces count twice; clean-mesh can remove duplicates and zero-area faces.

Why is the count higher than my CAD feature count?

CAD tessellation turns each curved surface into many triangles. The count depends on export tolerance; a finer tessellation gives a larger STL with the same design.

Inspect & measure/Face counts

STL triangle and vertex counter

Count triangles, welded vertices, and degenerate faces in an STL without sending the file anywhere. This is a fast way to see whether a mesh is too dense for a printer, a slicer, or a browser viewer.

ReadyNo uploadWorkerSTL

Tool facts

Formats: STL
Output: Report
Worker: Yes
Max file: 500 MB
Runs: in your browser

Why local

Drop an STL to see it here

Model

Drop an STL here

Binary STL streams in 4 MiB slices; ASCII STL streams line by line.

Choose a file

Max file size: 500 MB · No upload

No upload · File.slice() → dedicated Worker → transferable geometry.

How it works

1
Drop a binary STL into the drop zone.
2
The parser validates the declared triangle count against the file length.
3
It streams blocks, welds vertices, and skips zero-area triangles.
4
Read the counts and bounds, or open the same file in the STL viewer.

What the numbers mean

Triangles

Count includes every non-degenerate triangle emitted by the parser. Compare it with the declared count to spot truncated files.

Vertices

A closed surface usually has about half as many welded vertices as triangles. A ratio close to 3:1 means vertices were not shared by the source.

Degenerate faces

Zero-area triangles are skipped. A high count often follows a bad boolean operation or a decimation export.

Bounds

Check the three spans against the printer bed before slicing.

Printing notes

Above roughly 5 million triangles, slicers and browsers become uncomfortable; decimate before sharing.
A suspiciously low vertex count can indicate duplicate faces rather than a clean mesh.
Keep a copy of the original file; some repairs are easier to redo than to undo.

Questions

References

· Binary STL facet layout (50 bytes)
· ISO/ASTM 52900