ASCII knot
The same 9,216 triangles in two encodings. The sample files show the real byte difference without mesh simplification.
STL compressor
Make an ASCII STL smaller with binary encoding. See the actual size saving without simplifying the mesh.
Try:
Private · Free · No account
Open a file to preview and download.
Your file stays on this device.
Your model appears here
Open a file or try an example.
Same triangle surface. No mesh simplification.
Files you can inspect
Try an example above ↑Real input. Real output.
Already binary
A 51,284-byte binary STL. The tool reports no encoding saving and keeps the original bytes, including its header.
NASA wrench
An ASCII representation of NASA’s wrench shrinks from 4,354,314 to 728,284 bytes (83.3%). All 14,564 triangles remain. The binary NASA original itself has no encoding saving.
Source: NASA 3D Resources · NASA media usage guidelines
Quady3D samples and credited public models, processed with this converter. Images are renders of the actual sample meshes, rather than photographs of physical prints.
What changes in the file
- Smaller encoding
- ASCII text becomes compact binary STL: 84 header bytes + 50 bytes per triangle.
- Same triangle surface
- No decimation or smoothing. Coordinates use standard binary STL float32 precision; normals are recalculated.
- Already binary?
- Keep the original unchanged when binary encoding cannot reduce its size. No invented savings.
How to compress an STL
Open an STL
The tool identifies ASCII or binary from the file contents.
Compare the result
Review real byte counts, triangle count and dimensions. No geometry simplification is applied.
Download or keep original
Save a smaller binary STL, or keep your original when there is no size saving.
Questions about STL compressor
Is this STL compression lossless?
It does not remove triangles, smooth surfaces or simplify the mesh. ASCII coordinates are written as standard 32-bit binary STL values, so unusually high decimal precision may be rounded; facet normals are recalculated. Output coordinates are checked at float32 precision. Keep the ASCII original if you need its exact text or higher decimal precision.
Why does my binary STL not get smaller?
Binary STL already uses 50 bytes per triangle plus an 84-byte header. Re-encoding it cannot save much space without removing geometry. This tool keeps the original bytes unchanged. It does not claim a reduction when the result would be the same size or larger.
Does this reduce the polygon count?
No. This release changes file encoding only. Triangle count and dimensions are shown for comparison. It does not include mesh decimation, Draco, KTX2 or ZIP output; the download remains an STL for slicers.
Is this free, and are my files uploaded?
Conversion runs on your device in a browser worker. No account or generation credits are needed. Sample buttons download public examples; your own files are never sent to a conversion server. The limit is 100 MB of input and one million output triangles; smaller files work better on phones.