OneTaskBy Tim King · Updated
STL to OBJ
Convert 3D Print Files to OBJ, Free
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How the STL To OBJ works
This STL to OBJ converter takes a 3D printing file and writes it out as a Wavefront OBJ for modelling, rendering or game software. Drop a binary or ASCII .stl, check it stands the right way up in the viewport, choose whether to convert millimetres to metres and download the .obj. Everything runs in your browser and nothing is uploaded.
STL to OBJ: why convert at all
STL is the language of slicers: a flat list of triangles, each stored with its three corners repeated. OBJ shares corners between faces, stores vertex normals for smooth shading and is read by practically every modelling, rendering and sculpting program. Converting lets you texture, render or edit a printable part in tools like Blender, or hand it to software that will not open STL.
Up axis and units
STL files are almost always saved Z up, because printers build upwards along Z. Most modelling programs and the OBJ convention are Y up. Leave the menu on Z up and the model is turned so it stands upright in the OBJ; if it appears lying on its side in the viewport, the STL was already Y up, so switch the menu. STL has no units but is nearly always in millimetres. Choose mm to m for a game engine or renderer that works in metres, so a 120 mm part is 0.12 units rather than 120.
What the OBJ contains
One object with shared vertices, smooth vertex normals recomputed from the triangles, and the same faces as the STL. There is no material file, because STL carries no colour. The triangle count does not change, and the OBJ is usually a similar size to a binary STL and much smaller than an ASCII one.
FAQ
Will the OBJ open in Blender?
Yes. Use File, Import, Wavefront (.obj). Blender is Z up internally but its OBJ importer expects Y up files and rotates them, which is why the converter writes Y up by default.
Can I convert the OBJ back to STL later?
Yes, with the OBJ to STL converter. The round trip keeps the same triangles, so nothing is lost apart from the smooth normals, which STL does not store.
Why does my model look faceted?
Normals are recomputed across shared corners, but if the STL has every triangle disconnected, for example from some CAD exports, there is nothing to smooth across. The geometry is still correct; use your modelling program's merge by distance or shade smooth command after import.
See also: all Images tools, Units, Audio & Video, Documents, Data & Code.
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