Are my files uploaded to a server?

No. This conversion runs inside your browser using your own device’s processing power, and the file is not uploaded. Once a tool has been used once (video, text recognition and background removal download their engine from this site the first time), it keeps working when your connection drops.

Does the size stay right?

Yes. 3MF states its units and the geometry is written out at the same real-world scale, so the print comes out the size it was meant to be.

Why would I go from 3MF back to STL?

Because a slicer or a print service asked for STL. 3MF is the better format; STL is the one more places accept.

Convert 3MF to STL

Runs on your device · Your file never leaves your device.

3MF is the modern printing format — it holds colours, units and print settings that STL never could. But plenty of slicers and print services still ask for STL. This converts one to the other in the browser.

You are going backwards in capability on purpose, and the tool is honest about what that costs: colour and any print metadata in the 3MF do not survive into the STL, because the format has nowhere to keep them. The geometry and its real-world scale do survive, which is what the printer needs.

The conversion runs on your own machine, which for a 3D file is the whole point: a model is usually a client’s product, a scanned property or something not yet announced. Nothing is sent to a server, so there is nothing to delete afterwards and nothing to take anyone’s word for.

How to convert 3MF to STL

Drop the 3MF file — and its companion files if it has any.
Check that STL is selected.
Press Convert.
Download the STL file.

Supported formats and limits

Input: 3MF
Output: STL
Companion files: None — the 3MF carries everything
Keeps animation: No — the format cannot store it
Where it runs: In your browser; the model is never uploaded

Not for: Carrying print settings or colour — those are the reasons 3MF exists, and STL cannot hold them.

Everything on the build plate goes into one STL

The STL is built from the 3MF's build list. Every item on the plate is written at the position and rotation the 3MF gives it, so a plate with three parts becomes one STL holding three parts side by side. An object made of several components is assembled first. 3MF and STL both treat Z as up, so nothing is turned, and each part sits on the bed as it did in the 3MF.

The type the 3MF gives each object is checked. Objects marked as supports, or as "other", are left out of the STL, and the result says how many parts were left out. A beam lattice, the 3MF extension for lightweight struts, is built into solid struts, each an eight-sided tube.

Colour, names and settings

A 3MF can colour a model in three ways: materials with a display colour, a colour for each triangle, or a texture image. The tool reads all three, and the panel after converting counts the materials and textures it found, but none of them can be written to STL. Object names are lost as well. A binary STL begins with an 80-byte header that could hold a name, and this tool leaves it empty.

The size of the STL

A 3MF states its unit, millimetres unless it says otherwise. The tool reads it and writes the STL in millimetres, which is what slicers expect, so a part designed in inches comes out at the same real size. The page shows that size in millimetres before you convert.

Frequently asked questions

Are my files uploaded to a server?: No. This conversion runs inside your browser using your own device’s processing power, and the file is not uploaded. Once a tool has been used once (video, text recognition and background removal download their engine from this site the first time), it keeps working when your connection drops.
Does the size stay right?: Yes. 3MF states its units and the geometry is written out at the same real-world scale, so the print comes out the size it was meant to be.
Why would I go from 3MF back to STL?: Because a slicer or a print service asked for STL. 3MF is the better format; STL is the one more places accept.