Convert STEP to 3MF
Free STEP to 3MF converter that runs in your browser. See real dimensions before you download, and get a watertight, slicer-ready file.
Why convert STEP to 3MF?
STEP to 3MF is a handy shortcut for people who design in CAD and print on a modern slicer. 3MF keeps the unit, holds several parts in one file and stores colours, so a multi-body STEP assembly arrives in Bambu Studio, PrusaSlicer, OrcaSlicer or Cura as separate objects that you can arrange and set up individually. The conversion tessellates the exact surfaces with OpenCascade, and you can choose draft, normal or fine quality. Units in the STEP are respected and written as millimetres, so size matches your CAD. Colours defined in the STEP become 3MF base materials, which is useful for multi-colour printers. The parametric model, history and feature tree are not part of the output.
How to convert STEP to 3MF
- Drop your STEP file onto the converter — it opens in your browser, nothing is uploaded.
- Check the preview and the dimensions in mm; fix units or the up axis in “Units & orientation” if the size or orientation looks wrong.
- Choose 3MF as the output and click Convert. Several files download as one ZIP.
What carries over from STEP to 3MF
| STEP | 3MF | Result | |
|---|---|---|---|
| Colour / materials | Yes | Yes | Kept |
| Textures | No | No | — |
| Units stored in file | Yes | Yes | Written as mm |
| Separate parts | Yes | Yes | Kept |
| Usual up axis | Z | Z | Unchanged |
What changes
- Curved CAD surfaces are approximated by triangles at the chosen quality.
- Assembly parts become separate objects in the 3MF.
- STEP colours are kept as base materials; parametric features are lost.
- Textures are not applicable; STEP does not carry them.
Tips
- Use Fine quality for small parts with tight curves or threads.
- In the slicer, check that each part is oriented flat; CAD orientation is not optimised for printing.
- Delete non-printed items like hardware or reference bodies before exporting from CAD.
- Use the free print check if parts overlap or intersect in the assembly.
About STEP files
STEP, formally ISO 10303 and known as the Standard for the Exchange of Product model data, has been developed since the 1980s and is the main neutral format for moving CAD models between companies and systems. The usual application protocols are AP203 and AP214 for geometry and assemblies, and AP242 for modern product and manufacturing information. A .step or .stp file is plain text written in the EXPRESS-based Part 21 syntax. Unlike STL, it does not store triangles: it stores boundary representation (B-rep) geometry, meaning exact planes, cylinders, splines and NURBS surfaces joined by edges and faces into solids. That keeps holes perfectly round and dimensions precise, and allows the receiving CAD to keep editing faces. Files can contain assemblies, product structure, colours and units.
About 3MF files
3MF was designed by the 3MF Consortium, whose members include Microsoft, Autodesk, HP, Stratasys and Prusa, as a modern replacement for STL in additive manufacturing. A .3mf file is a ZIP archive following the Open Packaging Conventions. Inside it, an XML model part holds the mesh, while other parts can hold thumbnails, textures and metadata. Unlike STL, the mesh shares vertices between triangles, which makes files smaller and keeps the surface connected. The core specification defines units, build items with placement transforms, and several objects in one file. Extensions cover materials, slices and beam lattices. Bambu Studio, OrcaSlicer and PrusaSlicer save their projects as 3MF with their own settings stored in extra files, so a project from one slicer may open in another with the geometry intact but the print profile ignored.
3D printing notes
For multi-colour and multi-part prints, 3MF is the format to use. Bambu Studio and OrcaSlicer open each part as a separate object, which lets you assign a different filament or setting to each one, and Prusa-family slicers do the same. Because the unit is stored in the file, a model does not arrive at the wrong size. Be careful with project files: a 3MF saved by Bambu Studio carries printer, plate and process settings that PrusaSlicer will not apply, and some slicers pick a different default when a model has no declared plate. MeshShift writes 3MF with several parts and keeps colours as base materials, and it reads 3MF for viewing, measuring and print checks.
Frequently asked questions
Are the parts kept separate?
Yes. Separate bodies or components in the STEP become separate objects in the 3MF, so you can move, orient and print them individually.
Does 3MF keep the exact CAD curves?
No. Curves are converted into triangles. A finer quality setting gives smoother results at the cost of more triangles and a larger file.
Is this STEP to 3MF converter free and private?
Yes. The conversion runs in your browser with JavaScript and WebAssembly, so your STEP file is never uploaded to a server. There is no sign-up, no watermark and no daily limit; very large files are limited only by your device's memory.