Free tool
STEP to STL converter
Drop a STEP or IGES file from any CAD program. Get an STL or 3MF in millimetres, ready for your slicer.
Runs in your browser. Nothing is uploaded.
How to use it
1Drop the STEP file
A .step, .stp, .iges or .igs file from Fusion, SolidWorks, Onshape, FreeCAD, Inventor or any other CAD program. It is read on your device.
2Let OpenCascade mesh it
The first STEP file loads the OpenCascade reader (7.6 MB, cached after that). Every solid becomes a part in millimetres.
3Pick the parts
Each body in an assembly is listed with an edge check. Untick the parts you do not want, or keep them apart for multicolour printing.
4Download STL or 3MF
One merged STL, one STL per part in a zip, or a 3MF that keeps every part as its own object for Bambu Studio, OrcaSlicer and PrusaSlicer.
To convert a STEP file to STL, drop the .step or .stp file on the converter above, check the parts and their size in millimetres, and download an STL or 3MF. OpenCascade, the open-source geometry kernel used by FreeCAD, runs in your browser as WebAssembly and turns every solid into triangles, so the file never leaves your computer. IGES files work the same way.
Why STEP has to become a mesh
STEP (ISO 10303) is how CAD programs exchange exact geometry: a hole is a cylinder with a radius, a fillet is a surface with a formula. Slicers do not read that. They need a closed mesh of triangles, which is what STL and 3MF hold. Converting is called tessellation: every curved face is split into small flat triangles that stay within a tolerance of the true surface.
This converter sets that tolerance relative to the size of the model, 0.1% of the bounding box, with an angle limit for small curves. A 100 mm part is meshed to within about 0.1 mm, already finer than a typical FDM layer.
What comes through
| From the STEP file | In the STL or 3MF |
|---|---|
| Solids and their positions in the assembly | One part per solid, placed where they belong |
| The file's unit (mm, inch, metre) | Converted to millimetres, the unit slicers expect |
| Product and body names | Part names, kept in 3MF and per-part STL files |
| Curved faces | Flat triangles within the tolerance |
| Sketches, wireframes and drawings | Left out: they have no volume to print |
Before you slice
Every part gets an edge check after loading. Watertight means a closed volume, which is what CAD solids give. A part that shows open edges came from a surface model rather than a solid; repair it in the free STL repair tool or close it in CAD. To cut, hollow, add text or check overhangs before printing, open the file in the Depthue Studio STL editor, which imports STEP directly.
Other ways to convert STEP to STL
- FreeCAD: open the STEP, select the body and export it as STL; its import and export page lists both formats.
- Fusion: open the STEP and save the body as a mesh in STL or 3MF.
The converter above is quickest when you only have a browser, or when the file should not be uploaded anywhere.
Questions
How do I convert a STEP file to STL?
Drop the .step or .stp file on the converter above. OpenCascade, the open-source CAD kernel behind FreeCAD, turns each solid into triangles in your browser, and you download an STL or 3MF in millimetres. Nothing is uploaded.
What is the difference between STEP and STL?
STEP stores exact geometry: planes, cylinders, splines and the edges between them, so a hole is a true circle. STL stores only triangles. Converting STEP to STL approximates every curve with flat facets, which is what slicers need.
Is STP the same as STEP?
Yes. .stp and .step are two extensions for the same ISO 10303 format, and both open here. IGES (.igs, .iges) is an older CAD exchange format and works too.
Will the STL be accurate enough to print?
For most prints, yes. Curves are split so the facets stay within 0.1% of the model's average size from the true surface: about 0.1 mm on a 100 mm part, below what a 0.4 mm nozzle resolves.
What happens to an assembly?
Every solid becomes its own part at its assembly position. Download one merged STL, one STL per part, or a 3MF that keeps the parts separate.
Can I go back from STL to STEP?
Yes, with the STL to STEP converter, but only as a faceted solid: a mesh does not remember which triangles were a cylinder, so the STEP has one flat face per triangle.
Is my CAD file uploaded?
No. The file is read and meshed by WebAssembly in your browser tab. Nothing is sent to a server, which matters for client and production parts under NDA.
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