Convert STP to STL
Upload a .stp file and get a single binary STL triangulated from the STEP solid at a fixed 0.1 mm chord tolerance, with coordinates in millimeters so a slicer reads it at 1:1 scale. Colors, part names and assembly structure are not carried over.
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What changes when STP becomes STL
A .stp file is the three-letter spelling of STEP, the ISO 10303 exchange format CAD programs write when they need to hand over exact geometry: analytic planes, cylinders and NURBS surfaces stitched into solids. That is what makes it useful for machinists and for moving a part between CAD packages, and also what makes it useless to a slicer. Print preparation tools, mesh editors and online print services read triangle meshes, so an STP has to be tessellated first.
On this page the file is uploaded to our servers and opened by FreeCAD 1.1, whose OpenCASCADE 7.9 kernel reads AP203, AP214 and AP242 B-rep data. A few repairs run first: a gzip-compressed STEP is decompressed, UTF-16 text is re-encoded, a byte-order mark is stripped, a missing END-ISO-10303-21 terminator is added back, and a drawing-style STEP stored in a 2D context is lifted to z=0. The shape is then meshed at a linear deflection of 0.1 and an angular deflection of 0.5 radians (about 29 degrees) and written as a binary STL.
What survives is the shape and the scale. STEP length units are converted to millimeters on import, so a 25.4 mm hole stays 25.4 units wide in the STL and needs no rescaling in Cura, PrusaSlicer, Bambu Studio or Orca. What is lost is everything that is not a triangle: the exact surface math becomes flat facets that sit within roughly 0.1 mm of the true surface. If the STP holds several solids, they all land in one STL as separate shells rather than one fused body, so a slicer may list them as multiple objects.
This is the conversion to run when a supplier or a parts library only published a .stp and you want to print it, get a quote, or sculpt on top of it in a mesh editor. If you still need editable geometry downstream, keep the original STEP file, or convert it to IGES, which is written as real B-rep rather than triangles.
Step by step
- In your CAD program, export the part or assembly as a single STEP file with geometry included. An assembly that only references external part files carries no geometry of its own and will be rejected.
- Select or drop the .stp file here; the target is fixed to STL on this page. Guests can send up to 50 MB per file and 10 files per request, a free account 100 MB, Plus 200 MB and Pro 1 GB.
- Start the conversion. Processing runs on our servers, and most parts of a few megabytes finish within a few seconds of the upload completing; dense assemblies take longer, with a 10-minute ceiling per file.
- Download the STL. Links stay valid for about 4 hours, and each file in a batch is downloaded on its own.
- Open the STL in your slicer, check the bounding box against the CAD dimensions in millimeters, and run the mesh check or repair step before printing; several unfused shells from a multi-solid STP may show up as separate objects.
What this converter actually does
- Reads .stp and .step text Part 21 files (AP203, AP214, AP242) through FreeCAD 1.1 and OpenCASCADE 7.9, with no sign-up needed for the guest limits.
- Repairs common export damage before reading: gzip compression, UTF-16 encoding, a leading BOM, a missing END-ISO-10303-21 line, and 2D-context geometry that would otherwise sit off-plane.
- Converts STEP length units to millimeters, so the STL opens at real size in a slicer instead of 1000x off.
- Triangulates at a fixed absolute 0.1 mm chord tolerance and 0.5 rad angular tolerance, so curved faces stay within about a tenth of a millimeter of the original surface whatever the part size.
- Writes one compact binary STL holding every solid in the file, and rejects a result with no triangles instead of handing you an empty download.
Video Tutorial
An A-Z video guide on how to use MiConvert to change STP format to STL. This is the safest method to convert data without needing to download any applications to your device. 🔗 Format conversion too
Questions about STP to STL
What is the difference between an STP file and an STL file?
STP (STEP) stores exact boundary-representation geometry: trimmed surfaces and solids described mathematically, with units declared inside the file. STL stores nothing but a list of triangles with normals, in whatever unit the writer used. Converting is a one-way approximation: the triangles describe the same shape, but the surfaces, tolerances and any product structure are gone.
Is it lossless, and can I pick the mesh quality?
No. STL is always an approximation, and the tessellation here is fixed at 0.1 mm linear and 0.5 rad angular deflection with no quality slider. Colors, materials, part names and the assembly tree are not read from the STEP file at all. For custom deflection values, mesh the part in FreeCAD's Mesh workbench before exporting.
I got "Could not read this 3D file" - what now?
That generic message is the most common failure on this pair. It means the file was not readable as ISO-10303-21 text: usually a truncated or partially downloaded STP, an archive or binary file with the extension renamed, or a native CAD file such as .sldprt or .ipt saved under a .stp name. Re-export from the original program as STEP AP214 and upload again; most specific engine reasons are collapsed into two generic texts on the page.
Why does it say "No valid 3D geometry found"?
The usual causes are: the STP is an assembly skeleton that only references separate part files; the file holds only wireframe curves or sketch edges with nothing to triangulate; or a surface failed to tessellate. Re-export as a single file with geometry included. If the file genuinely holds only curves, convert it to DXF instead of STL.
Will the STL be watertight and ready to print?
The scale will be correct in millimeters, but we do not promise a watertight mesh. Closed solids usually tessellate into closed shells; parts built from unsewn surfaces can come out with cracks, and a multi-solid file arrives as several unfused shells. Run your slicer's or a repair tool's mesh check before printing.
Can I convert STP to DWG here instead?
No. We do not write DWG from CAD solids. The closest option is STEP to DXF, which produces a single automatic orthographic view of the visible edges on one layer, with no dimensions, title block, sections or multiple views. For a real drawing, place the views in your CAD program and export the drawing itself.
What happens to my file after the conversion?
The conversion runs on our servers, not in your browser. The uploaded STP is deleted as soon as the job's last attempt finishes, and the STL can be downloaded for about 4 hours before it is deleted automatically. File names, sizes and outcomes are logged for diagnostics, and signed-in users get a history entry; the download link is an unguessable random token and is not listed anywhere.