OBJ to STL Converter

Get OBJ models from Blender, ZBrush or an AI generator ready for your slicer: every face kept, quads split into triangles, standing up on the plate at a sensible size.

  • Files stay on your device
  • Free, no sign-up
  • Units and up axis handled
  • Batch and .zip

Drop an OBJ file to convert

One file, many, or a .zip

In: STL · STEP · IGES · OBJ · 3MF · GLB · glTF · PLY · FBX · DAE · 3DS · AMF · VRML · ZIP

Converted on your device. Nothing is uploaded.

    How to convert OBJ to STL

    1. Drop your OBJ files

      Drop the .obj with its .mtl and texture images, or a .zip of the folder.

    2. Check the preview

      The model appears at the size and orientation it will have. Fix the file units, up axis or size under Size, units and orientation if needed.

    3. Choose STL options

      Binary STL by default (smallest, read everywhere). Tick ASCII only if an old tool asks for text STL.

    4. Convert and download

      One file downloads straight away. A batch gives a download per file and one .zip of all of them.

    What carries over from OBJ to STL

    Worked out from what each format can store and what this converter writes. Nothing is changed silently: the preview shows the size and orientation before you download.

    Geometry Every face is kept; quads and n-gons are split into triangles.
    Color Dropped: STL cannot store color.
    Units OBJ has bare numbers, so they pass through as millimetres: 1 unit becomes 1 millimetre. If the preview size is wrong, set the file units.
    Orientation Turned from Y up to Z up, so it stands on the plate in a slicer.
    Objects Merged into one surface: STL has no objects.

    OBJ to STL: what actually happens

    OBJ is what Blender, ZBrush and AI generators hand you; STL is what every slicer and print service expects. OBJ to STL keeps every face, splits quads and n-gons into triangles, and drops what STL can't hold: materials, textures, UVs and vertex colors.

    OBJ has no units, so its numbers pass straight through as millimetres. If the model was built in metres (a Blender character 1.8 units tall would print 1.8 mm tall), the preview flags it and offers to read the file as metres. OBJ is also Y up by convention, so the converter stands it upright for the slicer's Z up; switch the up axis if your OBJ was already Z up.

    OBJ at a glance

    Wavefront OBJ · .obj

    Stores
    Vertices, faces (triangles, quads, n-gons), UVs and normals as text
    Color
    Materials and textures in a separate .mtl file; vertex colors as an unofficial extension
    Units
    None, the numbers are bare
    Up axis
    Y by convention (Blender, Maya, most 3D apps)
    File size
    Text: about a binary STL's size for bare geometry, up to twice that with UVs and normals
    Opens in
    Blender, Maya, 3ds Max, ZBrush, Cinema 4D, game engines, most slicers

    OBJ came out of Wavefront Technologies' animation software and became the plain-text lingua franca of 3D. The geometry is in the .obj; colors and texture references live in a companion .mtl file, which is why OBJs so often arrive grey.

    Open OBJ files in the viewer

    STL at a glance

    Stereolithography (Standard Triangle Language) · .stl

    Stores
    Loose triangles: three corners and a normal each, binary or ASCII
    Color
    None in the standard
    Units
    None written; slicers assume millimetres
    Up axis
    Z, the slicer convention
    File size
    50 bytes per triangle in binary, about 5 times that as ASCII
    Opens in
    Every slicer, CAD tool and 3D app

    Created by 3D Systems in 1987 for the first stereolithography printers, STL is still the format every slicer and print service accepts. It describes a surface as a list of independent triangles, with no shared vertices, units, colors or scene structure.

    Open STL files in the viewer

    Tips for OBJ to STL

    Skip the .mtl

    STL drops colors anyway, so the .obj alone is enough.

    Check it's watertight

    Sculpts and scans often have holes. Open the STL in the STL viewer for a mesh check, and fix it in Mesh Repair if needed.

    Keep the colors

    Printing in several colors? Convert OBJ to 3MF instead: material colors become filaments.

    OBJ to STL FAQ

    Why is my STL tiny or huge after converting from OBJ?
    OBJ stores numbers without units. A model built in metres reads as millimetres and comes out tiny. Set the file units to metres in the converter (it suggests this when the size looks wrong), or scale it in your slicer.

    Does OBJ to STL keep textures?
    No. STL stores geometry only. Use 3MF for filament colors, or keep the OBJ or GLB for textured renders.

    My OBJ has quads. Is that a problem?
    No. Quads and n-gons are split into triangles, which is what STL stores and what a slicer works with anyway.

    Is the converter free? Are there limits?
    Free, with no sign-up, watermark or file count limit. Batches and files of a few hundred MB work on most laptops; the only limit is your device's memory.

    Are my files uploaded?
    No. Files are read and written by JavaScript and WebAssembly in your browser and never sent to PrintPal. The STEP and IGES reader is the only extra download, once, from a public CDN.