STLBenchFree online 3D file converter
3D file converter — starting with what you were sent
Somebody hands you a .3mf, a .usdz or a .stp and the useful question is not "how do I convert this" but "what is it, and what should it become". This page answers both. Drop the file and it is identified, measured and described — triangles, millimetres, whether it closes, whether it carries colour — and the table further down says what each extension is for and which target suits which purpose. Then convert, in this tab, with nothing uploaded.
- 100% free
- No signup
- Format identified
- Ten extensions read
- 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 3D file
Three steps, and the first one happens before you touch the tool.
Find your extension in the table below
Before converting anything, it is worth knowing what you were handed. Half of the bad conversions in this field are somebody turning a file into a format that cannot hold the thing they cared about.
Drop the file and read what it actually contains
The panel measures it: triangles, bounding box, whether the surface closes, whether there is colour data, and for a STEP the real face count and the declared unit. That is the difference between what the format could hold and what your file does.
Pick the target the table suggests, and download
Every conversion prints the unit factor it applied and the specific losses for your model. If two targets look plausible, try both — switching does not re-parse the file.
Technical specifications
| Detects | Format from the file itself, not from its extension alone |
|---|---|
| Reads | STL · OBJ · PLY · 3MF · GLB · glTF · FBX · USDZ · STEP · STP |
| Writes | STL · OBJ · PLY · GLB · glTF · 3MF · USDZ |
| Reports | Triangles, size in millimetres, watertightness, colour data, declared unit |
| No reader for | .blend, .max, .skp, .dwg, .3ds — proprietary or licence-locked |
| Runs | Entirely in this tab; no upload, no queue, no account |
| File size | No fixed limit — past 100 MB you are told what it will cost this tab, then it opens |
Frequently asked questions
Somebody sent me a file and I do not know what it is.
Drop it in. The format is detected from the file rather than trusted from its name, and what comes back tells you whether it is a mesh or a CAD model, how big it is in millimetres, whether it carries colour, and whether it is closed. The table above then says what that format is for and which target makes sense. You do not need to guess before you start.
What is the safest format to convert to?
There is no universally safe one, and that is the useful answer. STL is accepted by the most software and holds the least — no unit, no colour, no parts. GLB holds the most and is accepted by browsers and engines rather than by printers. 3MF sits between them and is what a modern slicer prefers. The right target is decided by what you are about to do with the file, not by which format sounds standard.
Which format should I keep as the master?
Whatever came out of the software the model was made in. A STEP from CAD, a .blend from Blender, a .max from 3ds Max — the format that still contains the editing history, not the export. Every conversion on this site is one-way in the sense that matters: the information dropped does not come back, so convert copies and keep the original.
Why is my file rejected?
Three common reasons, and the message says which. A .gltf whose geometry lives in a companion .bin needs that companion — drop the folder or a zip and it is read from memory. A Draco-compressed glTF needs a decoder this page does not ship. And a format not on the list — .blend, .max, .skp, .dwg, .3ds — has no reader here, because each of those is either proprietary or licensed in a way that rules it out.
Can it convert CAD to mesh?
Yes, in that direction. A STEP or STP file is read as exact surfaces and tessellated into triangles, which can then be written as any mesh format. The reverse — triangles back into real CAD surfaces — is a genuinely hard problem and not something a page should claim casually; a converter that emits every triangle as a STEP facet is producing a file SolidWorks will choke on rather than a CAD model.
Is anything uploaded?
No. Detection, measurement and conversion all happen in this tab, whatever the format.
What each 3D file extension actually holds
The extension tells you which program wrote the file, not what is inside it. These nine are the ones that actually circulate, with what each carries and where it usefully goes next.
| Extension | What it holds | Usually convert to |
|---|---|---|
| .stl | Triangles only. No unit, no colour, no names — the printing lingua franca since 1987. | 3MF to gain a unit and a colour; OBJ or GLB to model or publish it |
| .obj | Text geometry with named groups and UVs; materials live in a separate .mtl. | GLB for the web, STL for a printer |
| .ply | A scanner's format: geometry plus per-vertex colour and any custom property. | STL to print it, 3MF to keep the colour |
| .3mf | Zipped XML with a declared unit, colours and a whole build plate of objects. | STL when something downstream is older than 2015 |
| .glb | One binary file holding a full glTF scene: meshes, PBR materials, textures. | STL to print, USDZ for iOS, OBJ for a modelling package |
| .gltf | The same scene as JSON — often pointing at a .bin and images beside it, which are read too. | GLB first, so it becomes one file that travels |
| .fbx | Autodesk's pipeline format: meshes, rigs, animation, cameras. Read-only here. | glTF to leave the closed format, OBJ for raw geometry |
| .usdz | Apple's AR package — a zipped USD scene with its textures. | GLB, so the asset works outside Apple devices |
| .step / .stp | Real CAD surfaces, not triangles, with the unit and assembly stated. | STL or OBJ once you accept tessellation |
The pattern in that table is worth naming. Formats differ far more in what they refuse to record than in what they record: every one of them stores triangles adequately, and they diverge on units, colour, materials, structure and whether a file can say what it is. Choosing a target is therefore choosing what you are prepared to lose, which is a decision about the next step rather than about the file.
Three extensions are missing on purpose. There is no .blend or .max reader because both are application-internal formats with no stable public definition. There is no .dwg reader because the only legal library is licensed commercially or under terms that would cover this whole site. Naming the gaps is more useful than a list of formats that silently fails on the one you have.
If you already know the pair, the converter page goes straight to the matrix, and the viewer opens a file without writing anything at all.
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.
One clause specific to this page: identifying an unknown file usually means it came from outside your organisation, and sending it straight back out to a conversion service is the reflex worth breaking. It never left — detection and conversion both run here.