STL to STEP Converter
Turn a 3D-printing mesh into a STEP file that CAD programs accept as a body. Every triangle of the STL becomes a flat face in the STEP, so you can measure it, add features to it or send it to someone who only takes STEP.
3D Model Converter
or drop STL, OBJ, MTL … files here ·
Max 95 MB per file· Up to 20 files· Deleted after 30 minutes
Files are processed on our servers and deleted after 30 minutes.
STL and OBJ store no units. If a part shows up 10× or 25.4× too small or too big in the slicer, the units were read wrong — set them here.
Blender, CAD programs and slicers use Z-up; glTF, Unity and most game engines use Y-up. Switch it if the model lies on its side after import.
Used when converting STEP or IGES solids to a mesh. Fine gives smooth curves but larger files; coarse is enough for quick previews.
Only used for PNG, JPG or SVG input. Relief raises dark areas; a lithophane is a thin panel that shows the photo when lit from behind; extrude turns a logo or SVG outline into a flat solid shape.
Width of the printed model; the height follows the image's aspect ratio.
Maximum raised height for a relief or lithophane, or the thickness of an extruded shape. Lithophanes usually use 2–3 mm.
Solid plate under the relief so the print holds together. 0 means no base.
How to use this tool
- 1
Upload the STL
Drop one STL or up to 20 at once, ASCII or binary, 95 MB each. Each file comes back as its own STEP file.
- 2
Tell it the units
STL carries no units, so open Advanced settings and set Model units to whatever the part was designed in. Millimeters is the default and is right for almost every printable model.
- 3
Convert and open in CAD
Press Convert to STEP, download the file and import it in Fusion 360, SolidWorks, FreeCAD or Onshape like any other STEP part.
Why an STL is not a CAD model, and what conversion changes
STL was created by 3D Systems in 1987 to feed the first stereolithography printers. It stores a list of triangles and nothing else: no units, no color, no curves, no record of how the part was built. That is all a slicer needs.
STEP, standardized as ISO 10303, comes from the other end of engineering. It describes a part with boundary representation (B-rep): exact planes, cylinders, cones and spline surfaces trimmed by edges, with units written into the file. When SolidWorks or Fusion 360 exports a bracket as STEP, the bolt holes are true circles of a known diameter.
Converting STL to STEP can only carry over what the STL has. The tool stitches the triangles into faces of one body, writes the unit you selected and closes the shell into a solid when the mesh is watertight. It cannot guess that 48 thin faces were once a single fillet, which is why this direction is mesh-to-B-rep wrapping, not reverse engineering.
- STL introduced by 3D Systems
- 1987
- First parts of ISO 10303 (STEP) published
- 1994
- STEP protocol that merges AP203 and AP214
- AP242
- Units stored in an STL file
- 0
STL
STL mesh
STL (stereolithography) is a 3D mesh format created by 3D Systems in 1987. It describes only the surface geometry of an object as a list of triangles, without colour, materials, units or scene information. Its simplicity makes it the default input for 3D printing slicers such as Cura and PrusaSlicer. Curved surfaces are approximated by many flat triangles, so smooth models can produce very large files.
- Compression
- –
- Transparency
- –
- Animation
- No
- Introduced
- 1987 · 3D Systems
STEP
STEP (ISO 10303)
STEP is an ISO standard (ISO 10303) for exchanging product data between CAD systems, first published in 1994. Unlike mesh formats, it stores precise solid geometry with exact curves and surfaces, plus assembly structure. It is the standard neutral format in mechanical engineering and manufacturing and opens in SolidWorks, Fusion 360, FreeCAD and other CAD tools. STEP files are not directly usable by 3D printers, which need a mesh such as STL.
- Compression
- –
- Transparency
- –
- Animation
- No
- Introduced
- 1994 · ISO
People convert STL to STEP when a CAD program, a client or a manufacturer insists on STEP and the only copy of the part is a mesh downloaded from a model library or exported for printing.
Editing a converted STL in Fusion 360, SolidWorks or FreeCAD
MythA STEP file is always editable like the original design.
FactA STEP file made from a mesh has no sketches or feature history. You edit it with direct modeling: push, pull, cut and add new features on top.
MythConverting to STEP makes the curves smooth again.
FactThe faces stay flat. Smoothness depends on how finely the STL was exported, and no file conversion adds detail that was never saved.
Once imported, treat the faceted body as a reference or a base. In Fusion 360 you can sketch on a flat face and extrude from it, or trace the profile and rebuild clean features over it. SolidWorks handles it as an imported body, so Move Face and cut extrudes work while dimension changes do not. FreeCAD's Refine shape merges coplanar triangles, turning a box made of 12 triangles back into six faces.
If you only need to view the part, print it again or check a measurement, you may not need STEP at all. STL to OBJ suits mesh editors such as Blender, and a printable copy with units and parts kept travels best as 3MF. Going the other way, from a real CAD solid to a printable mesh, is the routine direction covered on STEP to STL.
STL to STEP questions
Will the STEP file have smooth cylinders and fillets?
No. The converter keeps the exact shape the STL describes, and an STL describes every curve as a band of flat triangles. A hole printed from a 64-segment mesh arrives in CAD as a 64-sided prism. Smooth surfaces can only be recovered by remodeling them or with a reverse-engineering tool that fits surfaces to the facets.
Why does the STEP file have thousands of faces in the feature tree?
Each triangle becomes one planar face of the solid. CAD programs are built for parts with tens or hundreds of faces, so a mesh with 200,000 triangles is slow to rotate and select. In FreeCAD, Refine shape in the Part workbench merges coplanar faces, which shrinks flat areas to a single face each.
Can SolidWorks open the STEP made from my STL?
Yes. SolidWorks reads STEP AP203 and AP214 as imported bodies. Because the body has no feature history, you edit it with direct tools such as cut extrudes, holes and Move Face rather than by changing dimensions.
My STL is not watertight. Will the conversion still work?
Holes, flipped triangles or overlapping shells produce an open shell instead of a closed solid, and CAD programs treat that as a surface body. Run the mesh through your slicer's or modeler's repair tool first; PrusaSlicer and Windows 3D Builder can both fix common defects.
Which STEP version should I ask for?
Most tools read all three common application protocols. AP214 is the long-time default for mechanical parts, and AP242 is the newer edition that combines AP203 and AP214. For a faceted body from an STL, the version makes no visible difference.
Other mesh and CAD conversions
- STEP to STL ConverterConvert STEP or STP files to STL for Cura, PrusaSlicer and Bambu Studio. Pick coarse, normal or fine mesh detail and get a binary STL in millimeters.
- STL to OBJ ConverterConvert STL to OBJ for Unity, texturing tools and other 3D apps that expect OBJ. Shared vertices, readable text and the same triangles, in seconds.
- OBJ to STL ConverterConvert OBJ models from Blender, ZBrush or a scan into binary STL for 3D printing. Quads are triangulated, parts merged and the scale fixed to millimeters.
- 3MF to STL ConverterConvert 3MF to STL for slicers, print services and tools that only read STL. Geometry is kept in millimeters; colors, plates and print settings drop out.
- STL to GLB ConverterConvert STL print files to GLB for websites, model-viewer and Android AR. Millimeters scaled to meters and Z-up turned to Y-up so the part stands upright.