OBJ to STL converter

OBJ is the everyday file of 3D artists. Blender, ZBrush, Maya, Cinema 4D, SketchUp, scanners and game asset stores all export it. Printers and slicers prefer STL. This OBJ to STL converter turns the OBJ into an STL that stands the right way up and has the right size, and lets you check both before you download.

How to convert OBJ to STL

1. Drop the .obj file. You do not need the .mtl file or the textures: STL holds no colour, so only the geometry is used.
2. Check the size and orientation. OBJ files are usually Y-up, so the converter turns them Z-up automatically. If the size looks a thousand times too small, the OBJ was in metres; pick Metres under Source units.
3. Download STL. Tick Save each part as its own STL to get every object in the OBJ as its own file.

Why OBJ models arrive lying down

In most 3D animation and game software, Y points up. In CAD and 3D printing, Z points up. An OBJ exported from Blender with default settings, from Maya or from a game engine is written Y-up, so a printing tool reading it naively sees a figure lying on its back. The converter assumes Y-up for OBJ files and rotates them so they stand on the build plate. If your OBJ came from a CAD program or a scanner that already uses Z-up, choose Z is up under More options.

Getting the size right

OBJ files carry no units, only numbers. What those numbers mean depends on the program that wrote them. Blender writes metres by default, so a 5 cm figurine becomes 0.05, which a slicer reads as 0.05 mm. Maya uses centimetres. ZBrush uses its own internal scale that is often arbitrary. The converter shows the size it reads and warns you when it looks unlikely. Pick the correct Source units and the STL is written in millimetres at the true size.

If you do not know the intended size, scale to a target instead: download the STL, then open the STL scaler and set the height you want.

Is the model printable?

Artists' models are built to look right on screen, not to be solid. Watch out for:

• Single-sided surfaces such as leaves, hair cards and clothing planes. They have zero thickness and will not print. Add a Solidify modifier in Blender before exporting.
• Open meshes: a character with no inside of the mouth, or a building with missing walls. The STL repair tool closes small holes.
• Overlapping parts: eyes inside a head, buttons sunk into a coat. Slicers merge these when printing, so they are usually fine.
• Unapplied modifiers: subdivision, mirror or array modifiers only appear in the OBJ if you tick Apply Modifiers when exporting.

Objects and groups in the OBJ

An OBJ can hold many objects ("o" lines) and groups ("g" lines). Each becomes a separate part here. The size line shows how many parts the file has. Merged into one STL, they print as one model; saved separately, you can print a figure and its base in different colours, or skip parts you do not need.

OBJ files from popular programs

Where an OBJ comes from tells you what settings to expect:

• Blender exports OBJ with Y up and metres by default, and applies modifiers unless you untick it. A figure modelled 15 cm tall arrives as 0.15, so choose Metres in Source units here, or scale the model in Blender before exporting.
• ZBrush works in its own units, which have nothing to do with real sizes. Its 3D Print Hub plugin exports with a real size; for a plain OBJ export, set the height you want afterwards with the STL scaler.
• Photogrammetry tools such as Meshroom and RealityCapture export textured OBJ files at an arbitrary scale. The texture is dropped here; measure the real object and scale to match.
• Game asset sites usually offer OBJ next to FBX. These models are often hollow or open, so check them with the STL repair tool.

The converter reads quads and larger polygons and splits them into triangles, so you don't need to triangulate before exporting.

Updated November 2026 · How these tools work