What a Wavefront OBJ stores
Wavefront Technologies developed OBJ in the 1980s for its Advanced Visualizer animation software. The file is plain text, and each line starts with a short code: v for a vertex, vt for a texture coordinate, vn for a normal and f for a face. A face may be a polygon with more than three corners. Materials live in a separate .mtl file, and textures are images named inside it.
OBJ stores no unit. A model exported in metres, inches or centimetres looks the same in the file. Many models also arrive with Y as the up axis, while a printer bed expects Z.
How the OBJ file viewer opens it
Plain OBJ geometry is covered by tests: the mesh opens, converts and re-opens with the same size, volume and triangle count. To bring materials along, select the .obj, the .mtl and the images together in Open File, or drop them at once.
Materials and textures are handled by the engine but have not been tested by us yet. If colors look wrong, the geometry is still correct for measuring and printing.
Check an OBJ before printing it
- Open the .obj and read X × Y × Z in Info. A figure meant to be 120 mm tall that reads 4.72 was drawn in inches.
- Look at the mesh check. Watertight yes is what a slicer wants; open edges and holes go to Edit → Repair.
- Use Section to see whether a thin part is a closed solid or a single surface.
- Press Convert, choose STL or 3MF and tick "Rotate Y-up model to Z-up" if the model stands on its back.
Scale, orientation and size of OBJ meshes
| symptom | cause | fix |
|---|---|---|
| part is 25.4 times too small | drawn in inches | Edit → Inches → mm (×25.4) |
| part lies on its back in the slicer | Y-up export | "Rotate Y-up model to Z-up" on Convert |
| wrong size, unknown unit | no unit in OBJ | scale to an exact mm size on one axis |
| tab slows down | very dense mesh | reduce triangles to a chosen % |
The viewer shows OBJ numbers as millimetres. A 250k-triangle mesh opens in about 1.5 s; a million triangles take 5 to 12 s. For a lighter file, the STL simplifier cut a test sphere to 30 % with volume within 2 %.
An OBJ viewer for locked computers
School and office machines often block installers. This page needs only a Chromium browser, and JavaScript parses the mesh on your machine. The layout also works at phone width; it was checked at 390 px.
OBJ converters and related viewers
For printing, OBJ to STL is the usual route. OBJ to GLB packs the mesh into one file for the web, and OBJ to STEP writes a faceted body for CAD. The reverse, STL to OBJ, was tested on a 9,024-triangle sphere. Scans often arrive as PLY, which the PLY file viewer opens; game assets come as GLB or FBX. The OBJ file guide explains the format line by line.
Questions and answers
How do I open an OBJ file without Blender?
Drop it on this page in Chrome. You get orbit, zoom, section and measure, plus size and volume in the Info panel.
Why is my OBJ grey without its colors?
The .mtl and texture images were probably not opened with it. Select all of them together in Open File.
Can the OBJ reader check if the model is printable?
The mesh check reports watertight or not, holes, open edges, non-manifold edges and flipped triangles. Edit → Repair fixes the simple cases.
Is there a size limit for .obj files?
No fixed cap; memory sets the limit. Above roughly 1 to 2 million triangles the tab may run out of memory.
Can I open an OBJ file from a website link?
Yes. The Chrome extension counts 3D file links on a page, and a right-click on one gives Open in STL Viewer.
What does Wavefront mean in Wavefront OBJ?
Wavefront Technologies is the company that created the format for its Advanced Visualizer software. The file is the same .obj either way.