Starter
3credits
$7.99
$2.66 each
3 downloads of any size. Good for a one-off project.
Free under 5 MBSTEP → STLNo software installation
Convert STEP to STL online
Convert a STEP or STP (.step, .stp) CAD model to STL (.stl) for 3D printing, slicing and rapid prototyping. The converter tessellates CAD surfaces into triangles; always verify units, watertightness, facet density and thin features before printing.
Encrypted uploads Files up to 300 MB Automatically deleted within 7 days
Upload your STEP file
Choose one STEP file. This page is already configured to create STL output.
Drag and drop your STEP CAD file here
or choose a file from your computer
Browse filesMaximum file size: 300 MB
Files under 5 MB convert and download free. Larger files use one credit for one completed download, regardless of file size.
No STEP file available? Try a STEP sample to see the conversion workflow.
Pricing
Pay as you go, cheaper by the pack
Files under 5 MB convert and download free. Larger files use one credit for one completed download, regardless of file size. 1 credit downloads any file, any size, and credits never expire.
Save 11%
Pro
5credits
$12.99
$2.60 each
5 downloads of any size. The everyday choice.
Team
10credits
$19.99
$2.00 each
10 downloads of any size. Best balance of price and volume.
Studio
15credits
$26.99
$1.80 each
15 downloads of any size. Lowest price per file.
No desktop software
Start the STEP-to-STL workflow in your browser without installing a CAD application or conversion plugin.
Purpose-built mesh output
Create an STL for slicing and mesh workflows while keeping the original STEP as the editable engineering source.
Ready to inspect
Open the STL in a viewer or slicer to check scale, watertightness, triangle quality, surface smoothness and printability.
Open STL viewerPrivate file handling
Conversion files stay private, are not added to the public CAD library and are automatically deleted within 7 days.
Continue your workflow
Inspect the STEP, verify the STL or request specialist help
Inspect the STEP source, validate the generated mesh in the STL viewer and request design support when geometry needs repair before printing.
Check the source STEPConfirm that the source contains the expected bodies, surfaces and components before tessellation.Open STEP viewerInspect the STL outputInspect the mesh for holes, reversed normals, visible faceting, scale errors and missing thin features.Open STL viewerNeed a print-ready model?Ask a CAD designer to repair solids, add wall thickness, close gaps, orient parts or redesign features that are too thin for the chosen process.Hire a CAD designer
Simple conversion workflow
How to convert STEP to STL online
Move from a STEP solid or surface model to a tessellated STL mesh in three steps.
Upload the STEP file
Choose a .step or .stp file up to 300 MB. Ensure the source bodies are complete and correctly scaled.
Convert to STL
The route is preconfigured for STL output. Start the conversion without searching through a destination-format menu.
Download and verify
Open the .stl in the target slicer. Confirm the intended unit, dimensions, watertightness, orientation and mesh detail before generating toolpaths.
Format behaviour
What actually happens when STEP is converted to STL?
STEP stores CAD curves, surfaces, solids and product structure. STL stores only a triangular surface mesh. Conversion tessellates the STEP faces according to the engine's mesh settings. Curved surfaces become triangles, while assemblies, colors, names, materials, feature history and exact analytic geometry are not carried into standard STL.
What is normally retained
- Visible external shape within the tessellation tolerance
- Overall orientation
- Closed volumes when source solids tessellate correctly
- Separate shells or bodies where the exporter supports them
- Surface detail large enough to be represented by the mesh
What is not retained or may change
- Sketches, constraints and parametric feature history
- Exact cylinders, planes, NURBS and other analytic surfaces
- Assembly relationships, part names and product structure
- Colors, materials and most CAD metadata
- Explicit unit information in standard STL
STEP modelSTEP
STL meshSTLFormat comparison
STEP versus STL
Choose the format according to what the next application needs—not because one is universally better.
| Feature | STEP STEP | STL STL |
|---|---|---|
| Primary use | CAD exchange, manufacturing and engineering revision | 3D printing, slicing and mesh processing |
| Geometry | Exact B-rep curves, surfaces and solids | Triangular approximation of the surface |
| Editability | Can support CAD operations; native feature history still depends on source | Mesh editing with no parametric features |
| Units | Supports explicit units | Standard STL does not store a unit |
| Structure and metadata | Can contain assemblies, names, colors and product data | Normally only triangle geometry and normals |
Choose STL when
The next step is slicing or 3D printing
A mesh-based simulation or visualization tool requires STL
You have checked that the tessellation captures critical detail
You will keep the STEP as the engineering source
Keep STEP when
The design will be modified or manufactured from exact CAD geometry
Assemblies, names, colors or metadata matter
The receiving workflow accepts STEP directly
You need smooth analytic surfaces rather than a triangle approximation
Before continuing
Check the converted STL before using it
The STL must represent the shape at the correct scale and with enough mesh quality for the chosen manufacturing process.
- 01
Verify units and dimensions
STL has no standard unit field. Measure a known feature in the slicer and assign millimetres, inches or the intended unit.
- 02
Inspect curved-surface faceting
Zoom into arcs, holes and fillets to confirm that triangles are fine enough for the required finish.
- 03
Check watertightness and normals
Look for open boundaries, inverted faces, self-intersections and non-manifold edges.
- 04
Review thin walls and small features
Confirm that tessellation retained features near the printer's minimum wall and detail limits.
- 05
Confirm bodies and assemblies
Check whether multiple STEP components were exported as the required separate shells or one combined mesh.
- 06
Test in the target slicer
Generate a preview and inspect layer paths, supports, orientation and estimated print behaviour.
Common problems
STEP-to-STL troubleshooting
Most problems come from unit ambiguity, inappropriate tessellation, invalid source faces or features too small for the mesh and printing process.
Curves look visibly faceted
Cause: The tessellation is too coarse for the model size or required finish.
Fix: Use an export with a tighter chord tolerance, or rebuild the STL from CAD with controlled mesh settings.The STL is enormous
Cause: The mesh is finer than the workflow needs.
Fix: Reduce triangle density while preserving dimensional and curved-surface accuracy.The model is the wrong size
Cause: The slicer guessed a different unit because STL does not store one.
Fix: Select the intended unit or apply the correct scale before slicing.The slicer reports holes or non-manifold edges
Cause: Source surfaces did not form a clean closed solid or tessellation created invalid boundaries.
Fix: Repair the STEP body or heal the STL mesh before printing.Parts are merged or missing
Cause: Assembly components or hidden bodies were exported differently than expected.
Fix: Compare body count with the STEP source and export required parts separately.Small holes or walls disappeared
Cause: Features are below the tessellation or manufacturing resolution.
Fix: Use a finer export or redesign features for the target process.Secure processing
Your design files remain yours
Engineering files can contain confidential product geometry and documentation. Marathon OS keeps conversion uploads separate from its public CAD library and explains how each file is handled.
Encrypted transfer
Files are transferred over an encrypted connection.
Automatic deletion
Uploaded source files and converted outputs are automatically deleted within 7 days.
You retain ownership
Uploading or converting a file does not transfer ownership of the design to Marathon OS.
Never published automatically
Conversion files are not listed in the public Marathon OS CAD library.
Popular CAD conversion workflows
Explore a small set of adjacent engineering, mesh and drawing handoffs.
IGESSTEP
IGES to STEP
Legacy surfaces to modern CAD exchange
STLSTEP
STL to STEP
Mesh to CAD exchange
OBJSTL
OBJ to STL
Mesh handoff for slicing
3DMSTEP
3DM to STEP
Rhino to CAD/CAM exchange
DWGDXF
DWG to DXF
Drawing exchange
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Find an existing model before rebuilding one
Search the Marathon OS library for a usable starting model. Review dimensions, licensing and manufacturing suitability before using a downloaded file.
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Frequently asked questions
Frequently asked questions about STEP to STL conversion
Clear answers about output behaviour, compatibility, pricing, file limits and privacy.
How do I convert STEP to STL online?
Upload the STEP file (.step, .stp), confirm STL as the preselected output, start the conversion and download the STL result (.stl). Verify it in the application used for the next workflow.
Why convert STEP to STL?
Convert STEP to STL when the next workflow requires a triangle mesh—most commonly slicing and 3D printing—while retaining STEP as the editable source of truth.
How accurate is a STEP-to-STL conversion?
Accuracy depends on the tessellation used to approximate STEP surfaces with triangles. Inspect curved faces, dimensions and small features; for tolerance-critical work, use a controlled CAD export and record the mesh settings.
Which STEP and STL extensions are supported?
This route accepts .step, .stp input and creates .stl output.
Is the STEP to STL converter free?
Files under 5 MB can be converted and downloaded free. Larger files use one credit for one completed download.
What is the maximum STEP file size?
You can upload a STEP file up to 300 MB. Complex CAD and fine tessellation can create very large triangle counts and slower slicer performance.
How are my files handled?
Files are transferred securely, are not published to the public CAD library and are automatically deleted within 7 days. You retain ownership of the uploaded design.