Convert 3MF to STEP
A 3MF is a printing file. A STEP file is a CAD file. This conversion is the easiest one on this site to get right, for one reason: 3MF states what its numbers mean, so the part comes into CAD at the correct size without anybody having to guess. What you get is a faceted solid — a real solid CAD can work with, built out of flat faces.
Drag a 3D file here, or.
This page is set up for 3MF files. Other formats we can read work here too.
The file is read on your own computer. It is never uploaded.
Your file is read by your own browser and never sent to a server. There is no upload, no account and no copy of your model anywhere but on your computer.
The unit is in the file, so the size is right
Almost every mesh format records no unit. STL does not, OBJ does not, PLY does not. 3MF does: there is a unit attribute at the top of the model, and every slicer writes it. This tool reads it and sets the input unit box to match, so the measurements under the 3D view are the real size of the part before you touch anything.
That removes the failure that spoils most mesh-to-CAD conversions. If the 3MF says millimetres and you leave the output at millimetres, the STEP file will be exactly right. It is worth checking the numbers anyway, and they are on screen for that.
Slicer projects hold more than one thing
A .3mf from Bambu Studio, Orca or PrusaSlicer is usually a project rather than a model: the whole build plate, with every object on it, plus supports, settings and modifiers. Converting that to a single CAD solid is rarely what anyone wants.
So everything on the plate is listed above the 3D view with its own name and triangle count, and you choose. Isolate the one part you need, or keep them all and get one STEP file holding every solid. The 3D view shows immediately whether you picked the right one.
The tool also says which slicer wrote the file, which is worth knowing when a project turns out to contain a modifier mesh or a support blocker that you do not want in your CAD model.
Colour, and why it stops here
A 3MF can hold a colour per object and even per triangle, which is what makes multi-material prints work. STEP can carry a colour per face, and this writer does not put one there.
That is a deliberate choice. A colour written per face on a faceted solid multiplies the entity count for information no engineering process uses, and every CAD program shows an imported solid in its own default material anyway. If the colours matter, keep the 3MF: it is a better archive of a printable part than a STEP file is.
What this is actually for
You downloaded a printable part and need to design something that fits it — a mount, a case, an adapter. Import the STEP into CAD and build against the real shape.
You have a printed part in 3MF and a machine shop wants a CAD file to quote from. A faceted solid can be measured and sectioned, which is what a quote needs.
You are checking clearances in an assembly before printing. Solids mate and interfere; meshes do not.
You want to edit the design itself. That is the one this cannot do — there is no sketch inside a mesh to reopen. If the original CAD exists, ask for it; if it does not, draw the part again using the converted solid as your reference.
The merge, on a printing model
Printable models are frequently the best case for this converter. A printed enclosure, bracket or adapter is mostly flat panels, and every panel — however many triangles a slicer split it into — comes out as a single CAD face. Ratios of fifty or a hundred to one are common.
The number is reported under the download button so you can see what happened to your particular model. A high ratio means a small, clean file where clicking a wall selects a wall.
What survives, and what does not
Kept in the STEP file
- The unit the 3MF itself declares, so the part is the right size in CAD without guessing
- Every object on the plate, as separate named solids, or one of them on its own
- The shape, corner for corner
- Flat panels, merged back into one CAD face each
Lost on the way
- Colour and material assignments, which STEP could hold and this writer leaves out
- Everything a slicer project carries that is not geometry: supports, settings, modifiers
- Any parametric history — there is none in a mesh to recover
How to convert 3MF to STEP
Drop the .3mf in
A plain model or a slicer project, either works. If it is a project, the tool says which slicer wrote it and lists what is on the plate.
Pick the object you want
Use the isolate button on a row to take one part out of a plate of four. Keep them all to get every object as a separate solid in one STEP file.
Check the unit it declared
The input box is set from the file itself. Leave it alone unless the measurements under the 3D view are obviously wrong.
Convert and open in CAD
Read the merge report under the button. A printable part with flat panels usually drops by a factor of fifty or more, which means a file that opens instantly.
3MF and STEP compared
| Property | 3MF.3mf | STEP.step .stp |
|---|---|---|
| File contents | A ZIP archive holding XML. The model itself is one XML part inside it. | Plain text in the ISO 10303-21 exchange form. Readable, and enormous. |
| Geometry | Triangles, with a build platform and placement for each object. | Exact surfaces: planes, cylinders, cones, spheres, NURBS. Not triangles. |
| Units | Recorded in the file. Millimetre, centimetre, inch, foot, metre or micron. | Recorded in the file, as a full unit and tolerance context. |
| Colour and texture | Colour groups and materials per triangle, and textures in later extensions. | Colour per face or per solid, through the AP214 and AP242 styling entities. |
| Separate objects | Several named objects, each placed on the build plate with its own transform. | An assembly tree of named parts, each with its own placement. |
| Published by | The 3MF Consortium, 2015, explicitly to replace STL. | ISO 10303, from 1994. AP242 is the current application protocol. |
| Written by | PrusaSlicer, OrcaSlicer, Bambu Studio, Cura, Fusion 360 and Windows itself. | SolidWorks, Fusion 360, Inventor, CATIA, FreeCAD, Onshape — every serious CAD program. |
Questions
- Does the size come out right?
- Yes, and this is the one mesh format where that is true without you doing anything. 3MF states its unit and we read it. Check the width, depth and height under the 3D view all the same — it takes a second and catches a file that declared something odd.
- Is this a real CAD model I can edit?
- It is a real solid: your CAD program can cut it, add to it, measure it, section it and put it in an assembly. It is not a parametric model. There is no sketch to change, no extrude to edit and no dimension to type a new number into, because none of that is in a mesh to be recovered. If you need those, the model has to be drawn again from measurements.
- My 3MF is a Bambu Studio project with four objects on the plate.
- They are all listed above the 3D view. Isolate the one you want, or keep them all and the STEP file will hold four separate solids. Supports and modifier meshes are part of the project too, so check the list before converting.
- Can I keep the colours?
- No. STEP can carry a colour per face, but writing one on every face of a faceted solid bloats the file for information no CAD workflow uses. Keep the 3MF if the colours matter — it is the better archive for a printable part.
- Does my file get uploaded?
- No. The whole conversion runs inside your browser, and nothing is sent anywhere. That matters more here than on most pages: a part being taken into CAD is usually somebody’s product.
Where to go next
The other direction
Other things to do with a 3MF file
Other ways to get a STEP file
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