Open your 3MF
Choose an existing model or try a sample. The converter reads its declared unit, build objects and component transforms locally.
A CLEANER HANDOFF / FREE ONLINE CONVERTER
3MF to STL.
Know what you export.
Your model, in millimeters. Check dimensions and object positions before downloading a geometry-only STL. Free, with no account.
01 / Automatic unit conversion02 / Component positions retained03 / All or selected parts
01 — SOURCE FILE.3MF
Up to 50 MB · One file at a time · Local processing
Try a sample
Ready when you are. Your file stays in this browser.
02 — OBJECTS TO EXPORT
Original positions are kept. No mesh union or repair.
Import the result in millimeters. STL has no unit metadata.
MODEL INSPECTION
YOUR MODEL WILL APPEAR HEREX / Y / Z · mm
Dimensions · mm— × — × —
Triangles—
Selected objects—
i
Geometry makes the journey.
Colors, textures, materials and print settings do not. Review the exported STL in your slicer before printing.
Preview is an inspection aid, with detail sampled for large models. Every supported triangle is included in the download.
FROM FILE TO FINISHED HANDOFF
Three steps. One useful file.
Check the result
Review the millimeter dimensions and object placement. Select the parts you need. Original positions are preserved unless you choose to center them.
Download your STL
Export one combined binary STL, or a ZIP with an STL for each selected mesh instance. Open it in your slicer using millimeters.
A format change,
with clear boundaries.
3MF can carry an entire printing project. STL stores triangle geometry. Converting is useful when a service or older application asks for STL, but it does not preserve the full project.
This tool reads Core 3MF meshes and components, including build placement, rotation, scale and mirrored transforms. Source units from microns through meters are converted into millimeter coordinates. Same-unit cross-file production references are supported.
Not a mesh repair tool. Overlapping solids are not joined. Slicer projects with recognized negative parts or modifiers are rejected rather than flattened into misleading geometry. Unsupported required extensions, protected/alternative representations and mixed-unit cross-file models need export from the original application.
Safety limits: 50 MB input, 100 MB declared unpacked content, 32 MB per model/metadata part, 500,000 expanded triangles and 512 mesh instances. ZIP64 and encrypted packages are not supported.
1 centimeter in.
10 millimeters out.
The physical size stays the same. The numbers change because STL should be imported in millimeters. A two-part sample also checks that component placement survives conversion.
BEFORE YOU PRINT
A few useful answers.
Is this 3MF to STL converter free?
Yes. Conversion and both download options are free within the stated file limits. You do not need an account.
Are my files uploaded anywhere?
No. The conversion code runs in this browser and does not send model bytes, names or geometry to a server. See the privacy note below for ordinary website request logs.
Will the model size change?
The converter uses the source 3MF unit and converts coordinates to millimeters. For example, a cube with sides of 1 centimeter becomes 10 × 10 × 10 in STL coordinates. Import the STL as millimeters; STL itself has no unit field.
Can I export individual objects?
Yes. Select the mesh instances you need and download separate STLs in a ZIP. Component transforms are applied to each instance. Their positions remain shared unless you explicitly center the selection.
What happens to colors and print settings?
They are not included. Standard STL exports geometry only. Keep your original 3MF for colors, material assignments, supports and slicer settings.
Why was my slicer project rejected?
Some projects depend on negative volumes, modifiers, Boolean operations or extensions that cannot safely be flattened by this tool. Open the original project in its slicer and export the finished model as STL. A visible error is safer than a plausible-looking but incorrect model.
Your model stays yours.
Files and generated downloads are held in browser memory for this tab. Clearing the model releases the tool’s references; closing the tab ends the session. This page does not save models to browser storage, use a conversion API, or currently run advertising or analytics. Our web server records ordinary requests for site assets, including IP address and request metadata; model files are not uploaded or included in those requests.
If you choose to send feedback, only your message, category and optional reply email are sent to this server for the operator to review. No model or file name is attached automatically. Feedback is removed after 90 days by the service's periodic cleanup; the IP address is used temporarily for abuse prevention and is not saved with your message. Do not include passwords or confidential model details.
Only convert models you have permission to use. This independent tool is not affiliated with the 3MF Consortium or any slicer vendor. ZIP decompression uses fflate under its MIT license. Format behavior follows the 3MF specifications. Conversion does not certify printability.