STEP to STL Converter
Turn a STEP or STP part from Fusion 360, SolidWorks, Onshape or a supplier's catalog into an STL your slicer can print. You choose how finely the curved surfaces are cut into triangles.
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
Add the STEP files
Upload .step or .stp files, up to 20 at a time and 95 MB each. Assemblies are fine; every body in the file is meshed.
- 2
Choose the mesh detail
Open Advanced settings and set Mesh detail. Normal suits most prints, Fine is for visible curves such as knobs and enclosures, and Coarse is for quick test fits.
- 3
Convert and slice
Press Convert to STL, download the result and drag it into Cura, PrusaSlicer, Bambu Studio or any other slicer.
STEP to STL is the normal, one-way route from design to print: the exact CAD surfaces are sampled into triangles, and the only real decision is how many.
Why STEP to STL is a one-way conversion
STEP (ISO 10303) is the neutral exchange format of mechanical CAD. Its common application protocols, AP203, AP214 and the newer AP242, describe a part with boundary representation: a cylinder is stored as an axis and a radius, a fillet as a rolling-ball surface, and the file states whether its numbers are millimeters or inches. Any CAD program can rebuild exactly the same geometry from it.
STL, which 3D Systems introduced in 1987, has no curves at all. It is a list of flat triangles, each defined by three corner points and a normal, with no units. A slicer only needs that, because it cuts the model into flat layers anyway.
Meshing samples the exact surface at a chosen tolerance and keeps the samples. The cylinder becomes a ring of thin rectangles split into triangles, and the information that it was a cylinder is gone. That is why this conversion is routine, and why the reverse direction can never restore what was lost.
Choosing the mesh detail for a STEP file
- Coarse
Fewest triangles. Fine for fit checks, jigs and parts whose curves are hidden or sanded anyway.
- Normal
The default. Curves look smooth at typical FDM layer heights and the file stays small enough to slice quickly.
- Fine
Tighter tolerance for visible fillets, knobs, enclosures and resin prints, where facets catch the light.
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
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
People convert STEP to STL because slicers and print services work on triangle meshes, while the part was designed or supplied as an exact CAD solid.
Finer is not automatically better. Each step up multiplies the triangle count on curved faces, while flat faces stay at two triangles per rectangle whatever you choose. A large enclosure meshed at Fine can produce an STL several times the size of the Normal version, and on an FDM printer with a 0.4 mm nozzle the extra detail is usually below what the printer can reproduce. Resin printers, with much smaller layer heights, are where Fine pays off.
The output is binary STL by default: an 80-byte header, a triangle count and 50 bytes per triangle. Pick ASCII under File encoding only if a script needs to read the file as text, because the same mesh written as text is several times larger. If you are collecting STEP parts from a supplier archive, ZIP to STL converts the whole download in one pass.
Checks after converting STEP to STL
- Measure one known dimension, such as a hole diameter, as soon as the STL is in the slicer.
- Look at small holes and fillets in the preview; if they look polygonal, convert again at Fine.
- Check that the part sits flat on the bed; switch Up axis if it was exported lying on its side.
- Split or merge bodies to match how you want to print them.
- Keep the STEP file next to the STL so a later change starts from the exact model.
STEP to STL questions
Can I turn the STL back into an editable STEP later?
Not in a useful way. Meshing replaces every exact surface with flat triangles and throws away the curve definitions, so a later STL to STEP conversion gives a faceted body rather than the original part. Keep the STEP file as your master copy and export a new STL whenever the design changes.
Do I even need STL if my slicer opens STEP?
Recent versions of PrusaSlicer and Bambu Studio can import STEP directly and mesh it themselves. Cura does not read STEP without a plugin, and many print services, online viewers and older firmware tools still expect STL. Converting gives you one file that works everywhere.
Why do round holes print as polygons?
The mesh detail was too coarse for the hole size. Small features are the first to show facets because each edge is a larger fraction of their circumference. Convert again with Mesh detail set to Fine.
Does an assembly come out as one STL or several parts?
All bodies are written into the STL by default, positioned as they were in the assembly. Tick Merge into one mesh if you want a single object; leave it off when you plan to separate parts in the slicer, for example to print them in different colors.
What happens to colors and material names in the STEP file?
STL has no field for them, so they are dropped. If you need colors per part for a multi-material printer, convert to 3MF instead, which keeps separate objects and their colors.