STL to 3MF Converter

Drop an STL (or OBJ) and download a 3MF — converted entirely in your browser, never uploaded to a server. 3MF is what modern slicers actually prefer: it bakes the millimeter unit into the file so your model never imports 25× too big, it's manifold by specification, and it travels as one tidy package.

Drop an STL or OBJ file here

Your file is processed in your browser — never uploaded.

Open the editor →

Why convert STL to 3MF at all

STL is the lowest common denominator — just a bag of triangles, with no units, no color, and no guarantee the mesh is even closed. 3MF is the format the 3D-printing world moved on to, and Bambu Studio, PrusaSlicer, and Cura all open it natively. Converting gets you:

  • Unambiguous units. STL stores no unit, which is why a model so often imports microscopic or 25.4× too large. A 3MF declares millimeter in the file itself — what you exported is what your slicer loads.
  • Manifold by specification. 3MF requires a watertight, manifold mesh, so it surfaces problems up front instead of after a failed slice. This converter welds duplicate vertices and drops degenerate triangles on the way in.
  • Native to modern slicers. It's the default project/exchange format in Bambu Studio and PrusaSlicer — no "import legacy STL" detour.
  • One tidy package. A single self-contained file instead of juggling one STL per part.

One honest caveat

Converting an STL to 3MF does not add color — an STL never carried any, so there's nothing to recover. The body comes through with your slicer's default color. The 3MF color story is real, but it lives upstream: if you want a multi-color, AMS-ready 3MF, you need a model that has per-body colors to begin with. You can build one in Cadre's editor, color each body, and export a 3MF that carries those colors per body — see below.

Your file never leaves your browser

Plenty of "free online" converters upload your STL to a server, convert it there, and keep a copy around afterward. A few run locally now too, so "no upload" alone isn't the whole story. Here's the difference worth caring about:

  • It's the real geometry kernel, not a script. The same Rust kernel that powers Cadre's modeler is compiled to WebAssembly and does the conversion inside this tab. Your file is read, converted, and handed back as a download — it never goes to a server, and there's nothing to retain.
  • Spec-conformant output. The 3MF is built byte-for-byte against the 3MF Consortium Core specification — correct OPC package, namespaces, and plain-decimal coordinates — so slicers that read 3MF (Bambu Studio, PrusaSlicer, Cura) treat it as a standard file, not a "mostly works" approximation. A watertight mesh comes through as a solid model; an already-broken mesh comes through as a surface object, not silently faked into a solid.
  • No account, no quota, no watermark. Nothing is gated and nothing is stored, because nothing is sent.

How it works

Cadre is a browser-based CAD editor whose Rust geometry kernel runs client-side via WebAssembly. Drop a file and that same kernel imports your mesh, welds and cleans it, and writes a 3MF package — almost instantly for typical print-sized models. Large scans take longer because everything runs on your machine, not a server farm.

Want per-body color? Model it in Cadre

A converted STL is colorless, but a model built in Cadre isn't. Open the editor, add or import bodies, give each one a color, and export 3MF from the File menu — each body keeps its color in the package, ready for an AMS or any color-capable printer. For designing parts that print right the first time, the design rules that prevent failed prints are a good starting point.

FAQ

Does converting STL to 3MF add color to my model?

No. An STL stores only triangles — it never had color — so the converted 3MF comes through with your slicer's default color. To get a color 3MF you need a model that already has per-body colors; you can build one in Cadre's editor and export a 3MF that carries them.

Does my file get uploaded anywhere?

No. The conversion runs locally in your browser via WebAssembly. Your STL is never uploaded, never stored, and never retained — unlike many online converters, which upload your file to a server and keep the output for a while.

Is it free?

Yes — converting STL to 3MF is free, with no account, no upload, and no watermark on the output.

Why is 3MF better than STL for 3D printing?

3MF bakes in the millimeter unit (so models import at the right size), requires a manifold mesh, can carry color and material, and is the native format of Bambu Studio and PrusaSlicer. STL is the older lowest-common-denominator format that stores triangles and nothing else.

Will the 3MF open in Bambu Studio, PrusaSlicer, or Cura?

Yes. The output is built against the 3MF Consortium Core specification — a correct OPC package with the right content types and namespaces — so slicers that read 3MF, including Bambu Studio, PrusaSlicer, and Cura, treat it as a standard file.

Can I convert OBJ to 3MF too?

Yes — drop an OBJ instead of an STL and you'll get a 3MF back the same way.

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