3MF to STL

Converting 3MF to STL

1. Drop the .3mf onto the converter. Everything you need is inside the archive; there are no side files to add.

2. The preview shows all objects in their plate positions, with any colors stored as 3MF materials (colors painted in a slicer may not show). Check that every part you expect is there.

3. Convert and download the .stl. It's binary by default; switch to ASCII only if a tool insists on it.

3MF and STL are both Z-up, so there's no axis to fix. The model will sit on the plate in the same orientation it had in the 3MF.

Why convert 3MF to STL

3MF is the newer 3D printing format: a zip archive that can hold several objects, their placement on the plate, colors, materials and units. PrusaSlicer, Bambu Studio, Cura and Orca now save to it by default, and many model sites offer 3MF downloads. STL is the old format it was meant to replace, but STL still wins on compatibility.

You need 3MF to STL when the other end doesn't read 3MF: an older slicer or printer's bundled software, a resin slicer, a print service's upload form, a CAD or mesh tool, or a mesh-repair app. The converter does it in the browser, without uploading the file.

What the STL leaves out

3MF was designed to fix STL's gaps, so this direction always loses something. Know what before you convert.

Mesh geometry

Kept exactly. Both formats store triangles, and the coordinates are copied as they are.

Multiple objects

Merged into one STL, each in its plate position. STL has no notion of separate objects, so the slicer will see one model. If you need them separate, export each object on its own from your slicer.

Colors and materials

Lost. A multi-color 3MF becomes a single-color STL. You'll have to repaint or reassign filaments in the target slicer.

Units

3MF records its unit, almost always millimeters. STL has none, and the numbers are written unchanged, so a millimeter 3MF gives a correctly sized STL in any slicer.

Print settings, supports, modifiers

Lost. Slicer project 3MFs carry layer heights, painted supports, seams and modifier meshes in extra files the converter doesn't read. Only the model geometry is written.

Common problems

Most issues come from what 3MF can express and STL can't, or from slicer project files that hold more than a plain model.

Just want to look inside a 3MF first? Use the 3MF Viewer.

Objects are stuck together in the slicer

That's the merge. STL has one mesh per file. PrusaSlicer and Bambu Studio can split it again with 'Split to objects'; stock Cura cannot, though its Mesh Tools plugin can. Parts that touch will split as one.

Preview is empty or parts are missing

Some slicer project files store objects in ways a general 3MF reader doesn't follow, or the file holds only print settings with no meshes. Open it in the slicer it came from and export the plate as STL or as a plain 3MF.

Model is tiny or huge

Rare, but a 3MF can be saved in inches or centimeters. Check the size in the preview's info panel; if it's off by 25.4 or 10, scale it in the slicer.

Lattice or sliced 3MF won't convert

Beam lattice and slice extensions aren't read. Export the lattice as a mesh from the design tool first.

Should you convert at all?

If your slicer reads 3MF, keep using 3MF. It's smaller, it keeps colors and object separation, and it removes the guessing about units that STL is known for. Convert to STL only for the tool that actually needs it, and keep the 3MF as your master copy.

Have a 3D scan instead of a slicer file? See PLY to STL.