Compare OBJ Files — See What Changed

Why OBJ files are inconsistent to begin with

OBJ has been around since the 1980s and every 3D tool can export it, which is exactly the problem: two OBJ files from two different pieces of software can differ wildly in what they actually contain. Vertex normals are often missing (left for the importer to recompute), groups and materials may or may not be included depending on export settings, and — like STL — there's no explicit unit, so "1 unit" could mean a millimetre, a centimetre, or an inch depending on where the file came from. None of that is metadata you can trust when you're trying to answer "what actually changed between these two versions."

Comparing the geometry, not the file

Because OBJ's surrounding metadata is unreliable, a useful OBJ diff has to work the same way a useful STL diff does: ignore the file's own claims about materials or groups and compare the actual triangulated surface. Meshdiff voxelizes both OBJ meshes into a shared grid, classifies each voxel as added, removed, or unchanged, and layers a per-vertex signed-distance heatmap on top to show exactly how far a surface moved — the same pipeline used for STL and 3MF, so results are consistent across formats.

Where OBJ diffing shows up in practice

• Exports from sculpting or CAD tools that default to OBJ (Blender, ZBrush, some parametric tools' mesh-export path) rather than a print-focused format.
• Cross-tool pipelines where a model passes through more than one application before printing, and you need to confirm nothing shifted in the round trip.
• Scan-to-print workflows where a 3D scan exported as OBJ needs to be checked against a repaired or decimated version before sending it to a printer.

What to check in the diff

The same checklist applies as for any format: volume delta, bounding-box change per axis, hole diameter changes, minimum wall thickness (0.8mm for typical FDM setups), and any new unsupported overhang past 45°–55°. Because OBJ files can arrive without consistent units, it's worth a quick bounding-box sanity check first — if Version B suddenly reads as 25.4× larger than Version A, one of the two was very likely exported in inches instead of millimetres.

How to compare two OBJ files

Open the free diff tool, drop your two OBJ files into the Compare view, and Meshdiff runs the voxel and heatmap diff entirely in your browser — no upload, no signup.