Convert STL to STEP
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The STL to CAD converter for mechanical parts. Simple parts come back with true analytic planes and cylinders you can re-dimension; everything else gets an honest faceted conversion, never silently wrong geometry.
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How It Works
Upload Your STL
Drag and drop your .stl file. Free accounts support files up to 25MB.
BREP Conversion
The converter first looks for the part's underlying planes and cylinders. Three checks decide whether it can use them: the detected surfaces must cover at least 80% of the part, the rebuilt solid must match the mesh volume within 2%, and sampled points from the mesh must land on the rebuilt surface. That third check exists because a wrong shape can match the right volume by coincidence. Pass all three and you get true analytic CAD faces, including real cylinders for holes and rims. Otherwise FreeCAD's OpenCASCADE kernel sews the triangles into a solid. Below 50,000 triangles it also merges coplanar facets, so flat regions become single selectable faces; above that the merge is skipped, because on a dense organic mesh it runs for minutes and finds nothing to merge. Curved surfaces keep the mesh's faceting either way.
Download STEP
Get an editable STEP file you can open in SolidWorks, Fusion 360, FreeCAD, OnShape, or any CAD program.
When This Works Best
Great results with:
- Mechanical parts with flat faces and cylindrical features
- 3D printed brackets, mounts, and enclosures
- Simple geometric shapes — boxes, cylinders, spheres
- Parts you need to modify dimensions on in CAD
- Models created in FreeCAD, SolidWorks, or parametric CAD tools
May struggle with:
- Organic/sculpted shapes — figurines, characters, terrain
- Very high-poly meshes (1M+ triangles)
- Complex freeform surfaces — car body panels, aircraft
- Models from photogrammetry or 3D scanning
- Models with extremely thin walls or fine details
STL vs STEP — What's the Difference?
.STL — Triangle Mesh
STL files describe 3D geometry as a collection of triangles. Every surface — no matter how smooth — is approximated by flat triangular facets. This makes STL excellent for 3D printing (slicers expect triangles) but useless for CAD editing. You can't select a "cylinder" or change a "radius" because those concepts don't exist in the format — it's just triangles.
.STEP — Mathematical Surfaces (BREP)
STEP files store geometry as mathematical surface definitions — planes, cylinders, cones, NURBS surfaces. A cylinder is represented by its center axis and radius, not by hundreds of triangles. You can select individual faces, change dimensions, add fillets, and generate engineering drawings. STEP is the ISO 10303 standard — every professional CAD system supports it.
Want to go deeper? Read our full STL vs STEP comparison →