Browser-local converter

STL to 3MF converter

Convert an STL into a 3MF package locally. This is the one conversion here that gains information rather than losing it: an STL is unitless, and a 3MF declares its unit, so the size you set in the workspace is written into the file and stops being a guess.

Drop your STL files here

STL, OBJ, PLY, GLB, glTF, 3MF, SVG and DXF. Nothing is uploaded: files are read and converted inside this tab. Checking what this device can handle...

Queue

No files yet. Drop models above, or use the file picker.

Add a model to see it here.

Output

Convert toDXF and SVG need a 2D source. A mesh cannot become a drawing without choosing a projection, which is yours to decide, not ours to guess.Encoding

3MF has one encoding.

Units

Assign unitLabel the existing numbers. Nothing is rescaled.Convert unitRescales so the physical size stays the same.

Size and placement

ScalingOrientation

Rotate X°Rotate Y°Rotate Z°

Centre on bedCentres X and Y, and sits the model on Z=0.

Repair and cleanup

These can change the shape, so they need a before-and-after review before export.

Safe repairWelds duplicates, drops zero-area triangles and fixes winding. Never fills holes.Weld duplicate verticesRemove zero-area trianglesWeld tolerance

Vertices closer than this are merged.Merge all meshes into oneNormals

Inspection

Add a model to see its dimensions, mesh health and estimated volume.

What this STL to 3MF conversion does and does not do

An STL declares no unit, so the workspace cannot know what its numbers mean. You assign the unit, and that assignment is what gets recorded in the 3MF. Assigning the wrong one produces a confidently wrong file.
An STL is a flat triangle soup with three unshared vertices per triangle. Those are written through as-is unless you weld first, which typically cuts the vertex count by around two thirds and makes a much tidier 3MF.
STL has no colour or material data of any kind, so the 3MF is written with no base materials. Nothing is invented to fill the gap.
Vendor-specific per-facet colour extensions found in some STL files are not read, because they are not part of the STL format.
The 3MF is written with core specification geometry and materials only. Production, slice and beam-lattice extensions are not emitted.

Troubleshooting

My slicer still shows the wrong size

Check which unit you assigned before exporting. The 3MF records exactly what you chose. If the STL was authored in inches and you left the unit at millimetres, the 3MF now states millimetres and is wrong by a factor of 25.4.

The 3MF is bigger than I expected

Run weld before exporting. An unwelded STL carries three separate vertices per triangle and every one of them is written into the 3MF mesh.

The model has no colour in my slicer

STL had none to give. Colour has to come from somewhere, and inventing it would be dishonest. Assign materials in the workspace if you want the 3MF to carry a colour.

My old slicer will not open the 3MF

Some older firmware and slicers accept STL only. That is a reason to keep the STL, not a fault in the 3MF. Every 3MF written here is re-opened and checked before you download it.

Questions

Why convert STL to 3MF at all?

Because 3MF records its own unit, keeps objects separate, can carry colour and is a compressed package rather than a raw triangle dump. Almost every technical argument favours it; STL survives on compatibility alone.

Is the geometry changed?

No. The triangle count is preserved exactly and verified, and the declared unit of the output is checked as well as its bounds. Welding, if you choose it, changes the vertex count but not the surface.

Are two exports of the same file identical?

Yes. The archive is written with a fixed timestamp, so exports are byte-for-byte reproducible and the file carries no clock reading that could show when or where it was made.