Convert OBJ to STL
Free online OBJ-to-STL converter. No sign-up, no upload, no watermark — it runs entirely in your browser.
Drop your OBJ file here
or click to browse · we convert it to STL instantly
100% in your browser — your file never leaves your device.
Honest answer first: Cura, PrusaSlicer and Bambu Studio all open an OBJ directly, so you don't strictly need this page to print one. I still convert nearly every OBJ before it goes near a slicer, because an OBJ rarely arrives alone — it comes with a .mtl and a folder of textures the printer can't use, it's often split into groups the slicer will scatter across the plate, and half the mesh-repair tools worth using only speak STL. Two seconds here and I have one binary file with one solid in it, and everything downstream stops asking questions.
Converting Wavefront OBJ to STL (stereolithography)
OBJ is a simple, widely supported mesh format that can reference materials in a separate .mtl file. STL is the universal 3D-printing format. Converting OBJ to STL gives you a clean, single-file mesh ready for any slicer.
What's kept and what's dropped
The triangle geometry is preserved exactly. OBJ materials, UVs and the linked .mtl file are dropped — STL stores shape only.
What this conversion is actually for
A marketplace model with a .mtl in tow
A figure bought on CGTrader or pulled from Sketchfab lands as .obj + .mtl + four PNGs. For an FDM print the paint is dead weight, and the slicer will nag about the missing material file the moment the folder gets separated. Converted to STL it's one file I can drop on the plate, send to a friend or upload to a print service without the bundle falling apart.
A Blender export that's really three objects
I model brackets as separate objects and export one OBJ. PrusaSlicer and Bambu Studio both stop to ask whether that's one object with several parts, and the wrong click scatters the pieces across the plate. This converter writes every group into a single STL solid, so it lands as one part, positioned exactly as I left it in Blender.
Quads and n-gons from a modelling tool
OBJ can hold quads and big flat n-gons; STL can only hold triangles. Each slicer triangulates on import in its own way — this converter does it once, deterministically, so the wireframe I check in the STL viewer is the exact mesh the slicer will get.
Anything downloaded, before it's trusted
Nothing off Thingiverse goes to the printer until it has been through the STL repair tool for holes and inside-out faces. That tool — like Netfabb, Meshmixer's Inspector and most print checkers — wants STL, so the conversion is step one of the checklist rather than a chore.
How to convert OBJ to STL
- 1Drop your OBJ file onto the box above, or click to browse for it.
- 2Sculptor converts it to STL right in your browser — nothing is uploaded.
- 3Your STL file downloads automatically. That's it.
Before you trust the STL: 4 checks
- Size in millimetres
- OBJ has no units either, so the numbers carry over untouched. Open the result in the STL viewer: a figure that should be 60 mm reading 2.36 was modelled in inches (×25.4); reading 0.06 means metres (×1000). Fix it by typing the final size into your slicer's scale panel rather than guessing a percentage.
- One solid or several parts
- Every OBJ group is merged into one STL solid. If you need the parts separate — different colours, different infill, one part printed flat — split them in the slicer afterwards (PrusaSlicer: right-click → Split → To parts; Bambu Studio: Split → To objects) or export each group as its own OBJ first.
- Watertight?
- Game and render OBJs are often open shells with no bottom face. A format change can't fix that. Switch the viewer to wireframe, look at the underside, and run the STL repair tool if you see daylight.
- Inside-out faces
- STL normals are recomputed from each triangle's winding, so a face that was flipped in the OBJ stays flipped and renders dark. Most slicers cope; if a print comes out with missing walls, fix it in Blender first (Edit Mode → select all → Mesh → Normals → Recalculate Outside).
New to these formats? Read what an OBJ file is and what an STL file is. Check the result in the free STL viewer before it goes anywhere.
OBJ to STL — FAQ
- My slicer opens OBJ already — is there any point converting?
- For a single, clean, one-group OBJ you modelled yourself: not much. Convert when the OBJ comes with a .mtl and textures you don't need, when it's split into groups you want as one part, when a print service or repair tool only takes STL, or when you want a triangulated file you've already inspected instead of letting each slicer triangulate its own way.
- What happens to the .mtl file and the textures?
- They're never read. Only the .obj is parsed; the mtllib line is ignored and no image is opened. Keep the original bundle if you also render the model — an STL can't carry colour or UVs back out again.
- Does it keep my OBJ's groups as separate objects?
- No — STL has no concept of parts, so every group (every 'o' and 'g' in the file) is written into one solid at its original position. To keep parts separate, convert each group from its own OBJ, or split the STL in your slicer after import.
- Is the STL binary or ASCII?
- Binary, always. It's about a fifth the size of an ASCII STL of the same mesh (50 bytes per triangle instead of roughly 250) and every slicer and CAD package reads it. If a very old tool insists on ASCII, open the binary STL in your slicer and re-export.
- The STL opens at the wrong size — what went wrong?
- Nothing in the conversion: neither OBJ nor STL stores units, so whatever numbers were in the OBJ are in the STL, and slicers read them as millimetres. A part built in inches comes in 25.4× too small, one built in metres 1000× too small. Set the real size in the slicer's scale panel, or re-export from your modeller with units set to millimetres.
- Will it make the mesh watertight or fix holes?
- No. It changes the container, not the geometry — holes, overlapping shells and flipped faces come through exactly as they were. Run the converted STL through the free STL repair tool, which closes holes and reports whether the result is manifold.
- How large an OBJ can it handle?
- OBJ is plain text, so a 100 MB file is only a few million triangles and converts in seconds on a laptop; it all happens in your browser's memory and nothing is uploaded. Files in the hundreds of megabytes can exhaust the tab's memory — decimate first (Blender: Decimate modifier at 0.5) and you'll get a lighter STL the slicer will thank you for anyway.
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