STEP to STL converter, free and fully in your browser
Turn a STEP or IGES CAD model into a binary STL for 3D printing. Pick the tessellation, check the mesh in the preview, download. The file never leaves your computer: the OpenCASCADE kernel runs in your browser through WebAssembly.
Nothing is uploaded. The file is read and converted on your machine.
Add a file to start. The conversion engine loads when you do.
- Bodies
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- Triangles
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- Bounding box
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- STL size
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- Conversion time
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How it works
Three steps, no account.
Add your CAD file
Drop a .step, .stp, .iges or .igs file on the converter above. It is read in your browser, one file at a time.
Set the tessellation
Pick a preset or type the linear and angular deviation. The preview updates, so you can see how coarse or smooth the mesh is before you save it.
Download the STL
You get a binary STL in millimetres, ready for Cura, PrusaSlicer, Bambu Studio or OrcaSlicer. The bodies of an assembly are merged into one file.
Parameters
What goes in, what comes out and what you can set.
| Parameter | Value | Notes |
|---|---|---|
| Input formats | .step, .stp, .iges, .igs | One file at a time. The page checks the extension and, for STEP, the file header. |
| Output | Binary STL | 84 byte header, then 50 bytes per triangle. Coordinates in millimetres. |
| Linear deviation | 0.01 to 1 mm, default 0.05 | Largest gap between a triangle and the true surface. |
| Angular deviation | 0.1 to 1 rad, default 0.3 | Largest angle between the normals of neighbouring triangles on a curve. |
| Several bodies | Merged into one STL | The Bodies line shows how many were found. Names and colours are not kept. |
| Units | Converted to millimetres | Uses the length unit declared in the file. |
| Upload | None | The page sends no file and no model data anywhere. |
| Size limit | None set by the page | Very large models are limited by the memory your browser gives the tab. |
Why STEP to STL loses information
STEP stores exact surfaces. STL stores only triangles. The conversion goes one way.
| STEP (exact surfaces) | STL (triangles) | |
|---|---|---|
| A cylinder is | One true cylindrical face with a radius | Many flat triangles forming a prism |
| Holes and fillets | Real edges and faces you can select and change | More triangles, nothing to select |
| Accuracy | Exact within the CAD kernel tolerance | As close as the deviation you choose |
| Names, colours, assembly tree | Can be stored | Dropped, only the geometry remains |
| Typical use | Sending a part to a CAD user or a machine shop | Slicing and 3D printing |
Converting STEP to STL replaces every exact surface with flat triangles. The linear deviation sets how far a triangle may stray from the true surface, and the angular deviation limits how sharply neighbouring triangles may turn on a curve. In the measured example below, the 30 mm shaft measures 29.564 mm across X at 1 mm deviation and 30.000 mm at 0.01 mm, because every flat triangle on a convex curve sits slightly inside the true surface. Smaller deviation also means more triangles: the same shaft grows from 228 to 2,668 triangles, and the STL from 11.2 KB to 130.4 KB. Once the facets are finer than your printer can reproduce, extra triangles only make the file bigger.
Measured example
Five CAD files at the default settings (0.05 mm, 0.3 rad)
| Sample | Input | Bodies | Triangles | Box, mm | STL size | Time |
|---|---|---|---|---|---|---|
| Unit cube | 26.1 KB | 1 | 12 | 1.000 x 1.000 x 1.000 | 684 bytes | 456 ms |
| Enclosure, 2 bodies | 122.3 KB | 2 | 120 | 60.000 x 40.000 x 22.000 | 5.9 KB | 700 ms |
| Stepped shaft | 33.8 KB | 1 | 870 | 29.976 x 29.988 x 95.000 | 42.6 KB | 681 ms |
| Planetary stage, 5 bodies | 1.25 MB | 5 | 3,832 | 113.000 x 112.950 x 8.000 | 187.2 KB | 2.42 s |
| IGES cube | 11.3 KB | 1 | 12 | 10.000 x 10.000 x 10.000 | 684 bytes | 288 ms |
One part at four deviation settings
| Linear, mm | Angular, rad | Triangles | STL size | Width X, mm | Time |
|---|---|---|---|---|---|
| 1 | 1 | 228 | 11.2 KB | 29.564 | 614 ms |
| 0.1 | 0.5 | 576 | 28.2 KB | 29.951 | 608 ms |
| 0.05 | 0.3 | 870 | 42.6 KB | 29.976 | 639 ms |
| 0.01 | 0.1 | 2,668 | 130.4 KB | 30.000 | 644 ms |
Measured on 2026-10-07 in headless Chromium 149.0.7827.55 on an Intel Xeon Silver 4114 workstation. Time is the first conversion after the page loads (the engine download is not included), median of 3 runs per row. The stepped shaft is 30 mm in diameter and 95 mm long in the STEP file. Your times will differ.
Frequently asked questions
How do I convert a STEP file to STL?
Drop the .step or .stp file onto the converter at the top of this page, check the preview and press Download STL. The OpenCASCADE kernel reads the file in your browser, tessellates the surfaces into triangles with the deviation you set, and writes a binary STL in millimetres. There is no sign-up and no queue.
Is the STEP to STL converter free?
Yes. There is no account, no daily quota and no watermark on the output.
Is my file uploaded to a server?
No. The file is read inside your browser tab and converted by WebAssembly code that runs on your own machine. The page sends no file and no model data anywhere, which matters when the geometry belongs to a client or is under NDA.
Which tessellation settings should I use for 3D printing?
Start with the default Print preset: 0.05 mm linear deviation and 0.3 rad angular deviation. On the measured 30 mm shaft it gives 870 triangles and a width of 29.976 mm. Use Draft (0.5 mm, 1 rad) for a quick fit check and Fine (0.01 mm, 0.1 rad) for small round parts where facets would show. Fine produced 2,668 triangles for the same shaft, so use it only where it pays off.
What is the difference between STP and STEP?
None. Both extensions name the same ISO 10303-21 text format. The three letter .stp comes from systems that limited extensions to three characters. This converter accepts both.
Can it convert IGES files to STL?
Yes, it reads .iges and .igs files. IGES is older than STEP and often holds loose surfaces instead of solids. In that case the STL is an open shell, so check it in your slicer before printing. A 10 mm IGES cube converted to 12 triangles and 10 x 10 x 10 mm in the test.
Can I convert STL back to STEP?
Yes, with the STL to STEP converter. The STEP file it makes from triangles is free and is created in your browser. If you want an editable CAD model with planes, cylinders and holes recognised, Editable CAD on that page costs 4.90 EUR per file, after a free preview.
Why is the STL so much larger than my STEP file, or smaller?
The two formats store different things. A binary STL takes 84 bytes plus 50 bytes per triangle, so its size follows the triangle count, not the size of the CAD file. The 1.25 MB planetary stage in the test became a 187.2 KB STL with 3,832 triangles. Raise the deviation to shrink the STL.
Does the STL keep colours, names and the assembly structure?
No. STL stores geometry only. The bodies of an assembly are merged into one mesh and names, colours and the assembly tree are dropped.
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Part of the EduFacturing tool set.