# STEP to STL Converter

> Turn STEP and STP CAD files into STL for printing, right in your browser. OpenCascade meshes every solid at the quality you choose, assemblies stay in place, units come out in millimetres.

Page: https://printpal.io/convert/step-to-stl
Updated: 2026-11-12
Use it: open https://printpal.io/convert/step-to-stl in a browser and drop a file. Free, no account, files are processed locally and never uploaded.

STEP files describe exact surfaces, arcs and cylinders as math, not triangles. A slicer needs triangles, so STEP to STL is really tessellation: the converter runs **OpenCascade**, the geometry kernel behind FreeCAD, in your browser and lays triangles over every face of every solid.

The quality setting decides how closely the triangles follow the curves. **Normal** keeps the chord error within 0.05% of the part's size and starts a new segment at least every 20°, which won't show on an FDM print. **Fine** goes to 0.02% and 11° for small bores and fillets; **Draft** is for quick previews of big assemblies. Every body is placed where the CAD put it, in millimetres.

## How to convert STEP to STL

1. **Drop your STEP files.** Drop .step or .stp files. The STEP reader (about 7 MB) downloads the first time.
2. **Check the preview.** The model appears at the size and orientation it will have. Fix the file units, up axis or size under Size, units and orientation if needed.
3. **Choose STL options.** Binary STL by default (smallest, read everywhere). Tick ASCII only if an old tool asks for text STL.
4. **Convert and download.** One file downloads straight away. A batch gives a download per file and one .zip of all of them.

## What carries over

| | Result |
|---|---|
| Geometry | Exact STEP surfaces are tessellated into triangles with OpenCascade at the quality you pick (Draft, Normal or Fine). |
| Color | Dropped: STL cannot store color. |
| Units | Converted from the declared unit to millimetres, so it keeps its real size. |
| Orientation | Both are Z up, so it stays the right way up. |
| Objects | Merged into one surface: STL has no objects. |
| Editability | Feature history and exact surfaces are not recoverable from a mesh. Keep the CAD file as your master. |

## STEP at a glance (ISO 10303-21 (Standard for the Exchange of Product model data))

STEP is the ISO standard for exchanging exact CAD geometry. Unlike a mesh it keeps true curves, so a 10 mm hole stays a perfect 10 mm cylinder until something turns it into triangles.

- **Stores:** Exact B-rep solids: planes, cylinders, fillets and splines as math, in assemblies
- **Color:** Per part and per face in AP214 and AP242; none in AP203
- **Units:** Declared in the file, usually millimetres
- **Up axis:** Whatever the CAD used; usually Z
- **Meshing:** Needs tessellation into triangles before printing or rendering
- **Opens in:** SolidWorks, Fusion, Onshape, FreeCAD, Inventor, CATIA, NX; Bambu Studio, OrcaSlicer, PrusaSlicer

## STL at a glance (Stereolithography (Standard Triangle Language))

Created by 3D Systems in 1987 for the first stereolithography printers, STL is still the format every slicer and print service accepts. It describes a surface as a list of independent triangles, with no shared vertices, units, colors or scene structure.

- **Stores:** Loose triangles: three corners and a normal each, binary or ASCII
- **Color:** None in the standard
- **Units:** None written; slicers assume millimetres
- **Up axis:** Z, the slicer convention
- **File size:** 50 bytes per triangle in binary, about 5 times that as ASCII
- **Opens in:** Every slicer, CAD tool and 3D app

## Tips

- **Faceted holes?** Pick **Fine** and convert again: arcs are split at least every 11°, so a small bolt hole gets 32 or more sides.
- **Units** STEP declares its unit (usually millimetres) and the converter honours it, so the STL opens at the size you designed.
- **Keep the STEP** An STL can't be edited like CAD. Keep the STEP as the master; Bambu Studio, OrcaSlicer and PrusaSlicer can also import STEP directly.

## FAQ

### Is STEP to STL conversion lossy?

Yes, by design: exact curves become flat triangles. The quality setting controls how closely they follow; at Normal the deviation on a 100 mm part is about 0.05 mm, a quarter of a typical layer.

### Can I convert STP to STL too?

Yes. .stp and .step are the same format; drop either.

### Can it convert STL back to STEP?

Not meaningfully. A mesh has no exact surfaces to recover; tools that "convert" STL to STEP wrap each triangle as a flat face. Rebuild the part in CAD, or use FreeCAD's Part workbench if a faceted STEP is enough.

### Is the converter free? Are there limits?

Free, with no sign-up, watermark or file count limit. Batches and files of a few hundred MB work on most laptops; the only limit is your device's memory.

### Are my files uploaded?

No. Files are read and written by JavaScript and WebAssembly in your browser and never sent to PrintPal. The STEP and IGES reader is the only extra download, once, from a public CDN.

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