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3MF to STL Converter That Keeps Every Part

Convert a 3MF file to one binary STL or a zip of separate STLs without uploading the project.

  • Reads core 3MF and component-based Bambu or Orca project layouts.
  • Applies units and build placement before export.
  • Reports colour, settings, plates, and thumbnails that STL cannot keep.

Convert 3MF to STL in your browser

Output

Object names, triangle counts, millimetre sizes, and lost project data appear here.

Measured 3MF to STL sample

Measured on 2026-10-23 with the same parser and STL writer the converter above uses. The first file is our two-part sample plate (try it with the sample button). The others are public test files from the 3MF Consortium sample repository, including a production-extension file and a file built from components.

FileObjectsTriangles3MF bytesSTL bytesDropped
two-part-plate.3mf242,752386,4672,137,684colour data, print settings, 1 plate record
box.3mf1121,176684nothing
box_prod.3mf11210,017684nothing
components.3mf2601,5973,084nothing
multiple_cylinders.3mf65281,98126,484colour data
pyramid_vertexcolor.3mf141,261284colour data

Two things the table shows. On the two-part plate the STL is about 5.5 times the size of the 3MF, because a binary STL stores every corner of every triangle again while a 3MF stores each shared vertex once and compresses the XML. On the tiny box files the STL is smaller, since a 12 triangle STL is 684 bytes and the 3MF zip spends more than that on its own folder and XML wrapper.

Export STL from a slicer before converting

A 3MF can be either a neutral geometry package or a complete slicer project. If you already have the desktop app that created the file, direct export is often the shortest route. In Bambu Studio or OrcaSlicer, open the project, select the object or plate you need, and use the export command for STL. Check whether the command exports the selected object or every object. A multi-plate MakerWorld project can contain several arrangements, so repeat the export for each plate you intend to keep. Saving the project again is not the same action. Save preserves the 3MF project, while export creates triangle geometry for another program.

In PrusaSlicer, load the 3MF, select an object in the object list, and use Export as STL. PrusaSlicer can also export a plate as one mesh after placement. Cura normally treats imported 3MF geometry like another model on the build plate. Select the model and use its mesh export option if your version provides one. The exact menu label can change between releases, but the distinction stays useful: export the mesh when you need geometry, and save the project when you need printer, material, support, or slicing choices.

Use this browser converter when the original slicer is unavailable, when you want every printable component extracted at once, or when you want a clear report of what STL will discard. It reads the package locally and never applies the project's printer profile. If the resulting STL has open edges, run the geometry through the STL mesh repair tool. If it is too dense for an editor, use the STL triangle simplifier before continuing.

What changes between 3MF and STL

STL stores a triangle surface. It has no standard place for object names, colours, textures, filament assignments, printer profiles, support painting, layer settings, plates, or thumbnails. Conversion can preserve the visible solid geometry and its placed coordinates, but it cannot carry those project features into STL. This page therefore reports colour data, print settings, plate information, and a thumbnail when those entries are present. The report is a warning, not a promise that every vendor extension can be interpreted. Keep the original 3MF beside the STL if you may need to reproduce the sliced job later.

One merged STL keeps all printable parts at their build transforms. That is convenient when the placement itself matters, but disconnected solids remain disconnected inside the file. The per-object zip is better when you want to move, edit, or print pieces separately. A component-based Bambu or Orca project may store a small root model whose only job is to point at meshes under 3D/Objects. The converter follows those paths and applies component transforms before writing each STL. Items marked printable="0" are deliberately left out because the 3MF core specification says they are not part of the printable build.

Slicer helper volumes need the same care. Bambu Studio and OrcaSlicer store modifiers, negative volumes and support blockers as ordinary mesh parts and mark their role only in Metadata/model_settings.config. PrusaSlicer keeps them inside the object mesh and marks their triangle range in Metadata/Slic3r_PE_model.config. A plain converter that reads only the geometry would turn a settings box into a solid block in your STL. This one reads both config files, leaves those volumes out, and says how many it left out in the result panel.

File size, units, and multi-plate projects

A binary STL uses 84 header bytes and 50 bytes for every triangle. It repeats all three vertex positions for every face. A 3MF stores indexed vertices in XML and then compresses the package as a zip. Shared corners can be written once, and repeated XML compresses well. That is why an STL can be larger than the 3MF even though the STL contains less information. The measured sample above uses the same parser and binary STL writer as the live tool, so its byte counts are reproducible rather than estimates.

3MF also declares a unit. This reader converts micron, millimeter, centimeter, inch, foot, and meter coordinates to millimetres before export. STL has no unit field, so the numbers in the exported file are millimetre values by convention. An inch model with a width of 2 becomes 50.8 in the STL, not 2. This avoids the common result where a slicer interprets an inch-based design as a two millimetre object. The panel compares each extracted object with the selected printer bed, including a 90 degree turn on the bed.

Multi-plate projects need care. A vendor project can describe plate membership in metadata outside the core build list. The converter reports the detected plate count but exports the printable build geometry it can resolve. It does not recreate separate plate files or infer a slicer's private arrangement rules. Inspect the object list and dimensions before downloading. If plate-by-plate placement matters, open the project in its slicer and export each plate there. For the reverse workflow, the STL to 3MF converter creates a neutral, unit-aware package from meshes you already have.

When not to convert a 3MF file

Do not convert when the reason you downloaded the 3MF is its prepared print job. Filament mapping, painted colour regions, support blockers, modifier meshes, printer selection, temperatures, layer heights, and plate order can be more valuable than the triangle surface. Open that project in the intended slicer and review every imported setting instead. A project from another person should never silently replace the hardware profile you trust. Conversion to STL removes that risk, but it also removes the useful settings, so the right choice depends on whether you need the design or the prepared job.

Also avoid conversion as a supposed repair step. Repackaging triangles does not close holes, remove self-intersections, or make thin walls printable. It can expose parts in a format your repair program understands, but the topology is unchanged. If your source is OBJ instead, the OBJ to STL converter handles triangulation and reports materials that cannot survive. For a logo or flat outline, the PNG to STL workflow is a more direct starting point than forcing an unrelated 3MF through several conversions.

Conversion questions

How do I convert 3MF to STL?

Choose a .3mf file above, review the objects and the information that STL cannot keep, then download one merged STL or a zip with one STL per object. The conversion runs in your browser. Core 3MF meshes, build transforms, component transforms, declared units, and external object paths used by common slicer projects are applied before export. Colour assignments, printer settings, plate metadata, and thumbnails cannot be stored in STL, so keep the original 3MF whenever those project details matter later.

Can I convert a Bambu Studio or MakerWorld 3MF to STL?

Yes, when the archive contains readable mesh objects. Bambu Studio, OrcaSlicer, and many MakerWorld projects place meshes under 3D/Objects and reference them from a small root model. This converter follows those component paths and applies their placement transforms. It reports detected colour data, project settings, plate count, and thumbnails because STL cannot preserve them. A complex vendor project can contain private features outside the 3MF core specification, so inspect the exported object count and dimensions before relying on the STL.

Why is the STL larger than the 3MF?

Binary STL repeats three complete vertex coordinates for every triangle and uses 50 bytes per triangle plus an 84 byte header. A 3MF normally stores shared vertices once, describes faces by index, and compresses its XML files inside a zip archive. Repeated tags and coordinates compress especially well. The STL can therefore be much larger while containing less information. The samples table on this page is generated by running the same parser and STL writer over the included fixture, so its byte totals show the effect on a reproducible file.

Does 3MF to STL keep colours and print settings?

No. STL has no standard fields for filament colours, textures, printer profiles, process settings, painted supports, plate descriptions, or preview images. The converter preserves triangle geometry and applied placement, then lists the project information it detected and had to omit. A zip with separate STLs can keep parts separate as files, but it still cannot attach filament assignments to them. If you need to reproduce a prepared print job, open the original 3MF in its intended slicer and keep that project as the source of truth.

What happens to inches and other 3MF units?

The 3MF model declares its coordinate unit, unlike STL. This converter recognizes micron, millimeter, centimeter, inch, foot, and meter, and converts all geometry and transform translations to millimetres before writing STL. For example, a two inch width becomes 50.8 in the output coordinate values. Most slicers interpret STL coordinates as millimetres, so the physical size stays correct on import. The result panel shows each part size in millimetres and compares it with the selected printer bed to make an unexpected unit conversion visible.

Should I export one merged STL or separate STLs?

Choose one merged STL when the relative placement of all printable objects matters or when the destination expects one file. Disconnected pieces remain disconnected surfaces inside that STL. Choose the zip when you want to move, edit, assign, or print each object independently. The zip contains one binary STL for every resolved printable mesh. Neither option preserves slicer settings or colour. For a multi-plate project whose exact plate membership matters, direct export from the original slicer is safer because vendor plate metadata is not part of ordinary STL geometry.

Need to go the other direction? Use the STL to 3MF converter with named parts.

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Convert and prepare files

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    Extract printable parts from a 3MF as one STL or a zip.

  • STL to 3MF

    Combine printable meshes in a unit-aware 3MF.

  • OBJ to STL

    Convert between OBJ and STL in your browser.

  • STL simplifier

    Reduce triangle count while checking the resulting size.

  • Mesh repair

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