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STL3MF

STL to 3MF converter

Combine one or more STL files into a single 3MF with correct mm units, ready for your slicer.

  • Nothing uploaded
  • No sign-up
  • Free, no limits

Drop your STL files here

or paste it, or pick it from your device

.stl

  1. Drop your STL file
  2. Check it in 3D
  3. Download 3MF

Good to know

How to combine STL files into a 3MF

  1. Drop one or more STL files above. Add more any time.
  2. Check the preview and untick any files you don't want.
  3. Click Download 3MF. Each STL becomes a separate, named object in one file.

Why convert STL to 3MF?

  • One file instead of many. A multi-part print (a model with separate pieces or colours) travels as a single file.
  • Units are stored. 3MF records millimetres, so the model doesn't open tiny or huge in the next program.
  • Objects stay separate, with their names, ready to arrange or assign to filaments.
  • Smaller files. 3MF stores connected meshes and is compressed. In our tests the Stanford bunny went from 3.5 MB as STL to 1.1 MB as 3MF, and a 59,000-triangle vase from 2.9 MB to 0.66 MB.

Multi-colour prints from several STLs

Many models come as one STL per colour. Combine them here and open the 3MF in your slicer. When you load several files at once, slicers may ask: Bambu Studio says “Load these files as a single object with multiple parts?” and PrusaSlicer asks a similar question for multi-material printers. Answering yes keeps the pieces aligned as one object, with a part per colour you can assign a filament to.

STL has no units, so every program assumes millimetres. If a part was designed in inches, it will look 25.4× too small: see STL in inches vs millimetres.

One place 3MF doesn't help: Tinkercad can't import it. To make a big STL smaller for Tinkercad, reduce its triangles instead.

What is a 3MF file?

3MF (3D Manufacturing Format) was created in 2015 by a group including Microsoft, Autodesk, HP and Shapeways as a modern replacement for STL. Under the hood a 3MF is a ZIP archive with XML inside. It stores:

  • Units: millimetres by default, so models open at the right size.
  • Several objects, each with a name and position.
  • Colours and materials.
  • Compact, connected meshes, so files are usually much smaller than STL.

Bambu Studio, PrusaSlicer and OrcaSlicer also save whole projects as 3MF, adding their own extras: build plates, print settings and painted colours. Those extras aren't part of the 3MF standard, which is why a project from one slicer doesn't always open fully in another.

Need STL again later? Convert 3MF to STL.

Questions

How do I merge several STL files into one?

Drop all the STL files into the tool at the top of this page and download the 3MF. Each STL stays a separate, named object inside one file, in its original position.

Why convert STL to 3MF at all?

3MF keeps units (millimetres), separate objects and names in one smaller file, which makes multi-part and multi-colour prints easier to share and open.

Will the parts stay aligned?

Yes. The STL coordinates are kept exactly, so parts designed to fit together stay in place, ready to load as one object with multiple parts.

Does the 3MF include print settings or colours?

No. STL files have no settings or colours to carry over. Assign filaments and settings in your slicer after opening the 3MF.

Is 3MF smaller than STL?

Usually by a lot, because 3MF stores each corner once and is compressed. In our tests the same models were 3 to 4.5 times smaller as 3MF than as STL.

Are my files uploaded?

No. Everything happens in your browser, so your STL files never leave your device.