STLBenchFree online CAD to STL converter
CAD to STL, with the unit read from the file
Drop a .step or .stp and get a mesh a slicer will take. Two things decide whether the print is right, and both are on screen before you download: how densely the curves were sampled, which here follows the size of the part instead of a fixed number, and which unit the file says it was drawn in — the one an STL cannot carry and the reason a part can arrive 2.54 times too large. If what you were sent is a native file like .sldprt or .catpart, no browser opens those; the answer is below rather than pretended away.
- 100% free
- No signup
- Unit read, not assumed
- Tolerance scaled to the part
- Nothing uploaded
Drag a file anywhere on this page to open it. F fits the view, W switches shading, G the grid, R spins it.
How to convert a CAD file to STL
Three steps, and the first one saves the most time.
Check what you were sent
A .step or .stp is the neutral exchange format and opens here. A .sldprt, .ipt, .catpart or .prt is a native file that only its own package can read — nothing in a browser will open one, and the fix is to ask for a STEP rather than to hunt for a converter that claims it can.
Drop the file
Every surface in it is evaluated as the mathematics it actually is before a single triangle is emitted, and how densely it is sampled follows the size of the part — which is why a hydraulic fitting and a machine frame both arrive usable rather than one of them blocky.
Read the unit, then download
STEP states its unit; STL states none. The panel reports what the file said and what the model measures, which is the check that catches an assembly authored in inches before it reaches the print bed at 2.54× the size.
Technical specifications
| Reads | .step, .stp — AP203, AP214, AP242, assemblies included |
|---|---|
| Writes | .stl — binary, millimetres, welded vertices |
| Tolerance | About 1/1000 of the model's largest dimension |
| Unit | Read from the file, including CONVERSION_BASED_UNIT |
| Not readable anywhere in a browser | .sldprt, .ipt, .catpart, .prt, .dwg — ask for STEP |
| Flat drawings | DXF and SVG need a thickness — that is the DXF to STL page |
| Kernel | None — no OpenCascade, no WebAssembly, no server |
| Verified | 11 fixtures against OpenCascade: exact face counts, volumes within 0.7% |
| File size | No fixed limit — past 100 MB you are told what it will cost this tab, then it opens |
Frequently asked questions
My file is a .sldprt / .ipt / .catpart. Can you open it?
No, and neither can anything else that does not license the format. Those are native files: proprietary, versioned, and readable in practice only by SolidWorks, Inventor and Catia respectively. Sites that advertise them either run the real software on a server — you are uploading a confidential part to somebody's render farm — or they fail after you wait. The reliable move is to go back to whoever sent it and ask for a STEP. Every one of those packages exports one in two clicks, and it is what STEP exists for.
What about a DWG or a flat DXF?
Those are drawings rather than solids, so the conversion is a different operation: a flat outline has no thickness, and turning one into a printable part means choosing one. That is on the DXF to STL page, where you type the thickness and the holes are read as holes. DWG itself is AutoCAD's native format and is not read here — exporting it to DXF from AutoCAD or any of its compatibles is a single command.
What is lost converting CAD to STL?
The ability to change anything. Dimensions stop being parameters and become distances between vertices; a bore stops being a feature with a diameter and becomes a ring of flat strips; the structure of an assembly flattens into undifferentiated triangles. None of that is a defect in the converter — a slicer has no use for a surface equation and needs a closed mesh — but it is a door that only opens one way, so the original file is the one to archive.
How fine is the tessellation?
Proportional to the part rather than fixed in millimetres. The sampling is set so that the gap between a curve and the flat strip standing in for it stays around a thousandth of the model's own size, which keeps the result honest across four orders of magnitude of part. A fixed setting cannot: whatever number smooths a machine frame turns a small fitting into a file too heavy to slice, and whatever number suits the fitting leaves the frame visibly faceted.
Will the print come out the right size?
If the unit was read correctly, yes, and that is why it is on screen rather than assumed. STEP can declare millimetres, inches or a conversion factor from metres, and all three appear in real files. The panel names what was found and shows the resulting bounding box, so the sanity check is one glance: a bracket that reads 300 mm across was authored in inches and needs saying so before it is sliced.
Is my file uploaded?
It is not. Every stage happens inside the browser, from reading the file to writing the mesh. That is unusual in this category for a structural reason: most CAD converters are a web form in front of real CAD software running on a machine somewhere, and your part has to reach that machine for the conversion to happen at all.
There is no such format as CAD
The phrase covers two quite different kinds of file, and knowing which one is in your downloads folder decides everything that follows. Native files — .sldprt, .ipt, .catpart, .prt — are the working documents of one package, proprietary and versioned, and they are readable by that package and effectively nothing else. Neutral files — STEP, and its identical twin STP — exist precisely because that is intolerable in an industry where the supplier and the customer never use the same software.
So a converter that claims to open native formats in a browser is doing one of two things. Usually it is uploading your file to a server running the real application under licence, which means a confidential part now sits in a queue on somebody else's machine, retained for as long as their policy allows. Occasionally it is simply failing after a progress bar. The two-click export to STEP from the package that owns the file is faster than either, and it is the format the whole industry agreed on for exactly this.
Once it is a STEP, the conversion has two decisions in it and both are visible here. The tolerance, because triangles can only sample a curve and how finely they sample is a choice — a fraction of the part rather than a fixed number, so it behaves the same on a fitting and on a frame. And the unit, which is where the real mistakes happen: STEP declares one and STL declares none, so a file authored in inches becomes a file of bare numbers that the next program reads as millimetres. The panel names the unit it found before you download anything.
If you want to look before converting, the STEP viewer opens the same file without converting it at all; if the destination is a renderer rather than a printer, STEP to OBJ is the better file; and if what you hold is a flat drawing, DXF to STL gives it the thickness it does not have.
Where the conversion happens
Every number on this page is worked out by JavaScript running in the tab you are reading it in. The model you open is read straight off your own disk — it is never uploaded, logged or kept, which is also why these tools carry on working after you disconnect from the network.
The reason so many CAD converters require an upload is structural: they are a form in front of real CAD software running on a machine you do not control. The STEP reader used here was written for this site in plain JavaScript, so the file never has to go anywhere — which is also why the result appears the moment you drop it.