Compress STL meshes in your browser
ASCII to binary is the usual five-times win. Optional vertex rounding and a cleared header take a little more off files that are already binary.
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No STL to hand?
How to compress an STL
ASCII or binary. The mesh is read in this tab and never uploaded.
That is the conversion that turns a huge text dump into a compact binary mesh.
You get a valid STL with the same triangles. Check a print preview if you lowered precision a long way.
Why ASCII STL files are so large
STL is the common mesh exchange format for 3D printing: a list of triangles, each with a normal and three vertices. Nothing in the format compresses those numbers. ASCII STL writes them as text, with words like facet, normal and vertex on every line. Binary STL stores the same data as IEEE floats at a fixed fifty bytes per triangle plus an eighty-byte header.
That is why an ASCII exporter can produce a file several times larger than the same mesh saved as binary. Converting is lossless for the triangle list: the counts match, and a slicer sees the same facets. Rounding vertex floats is optional and is the only step here that can change geometry.
If the mesh is for the web rather than a printer, GLB is usually the better container: one file, scene graph, materials and far better compression options. This page stays on STL because that is what many CAD and slicer workflows still require.
STL compression FAQ
Why is my STL file so big?
Usually because it is ASCII. Every triangle is written out as text with keywords repeated on every facet. The same mesh as binary is typically several times smaller with no change to the triangles.
Is ASCII to binary lossless?
Yes for the triangle list. Binary STL stores the same normals and vertices as 32-bit floats. Optional vertex precision rounding is the only setting here that deliberately changes numbers.
Will my slicer open a binary STL?
Almost every current slicer and CAD tool reads binary STL. Turn off Force binary only if you have a specific tool that still demands ASCII.
Can you compress an STL with Draco?
Not inside an STL. Draco lives in glTF/GLB workflows. If you can leave the STL format, convert to GLB and compress there instead.
Do my files get uploaded?
No. Parsing and rewriting run in this browser tab. There is no upload endpoint for the mesh.
Related
Same format joins the queue. Anything else re-routes to its own tool.