Mesh Inertia Calculator — mass, center of mass, and inertia tensor from STL/OBJ
Free online inertia tensor calculator: upload an STL or OBJ mesh, pick a material density or target mass, and get mass, center of mass, and the full inertia tensor integrated from the actual geometry — plus ready-to-paste URDF and MJCF inertial blocks. Also fixes mm/cm-scaled meshes.
kg/m³
kg
What gets computed (not guessed)
| Property | Typical manual workflow | This tool |
|---|---|---|
| Mass | Weighed, or a round number picked | Volume integrated from the mesh × density (or density solved from a target mass) |
| Center of mass | Often left at the link origin (wrong for offset geometry) | Integrated from the actual triangles (divergence theorem) |
| Inertia tensor | Copy-pasted from a similar-looking part | Full 6-component tensor about the COM, from the real geometry |
| Non-closed mesh | Silently produces garbage numbers | Detected via the volume integral and refused with a warning |
This reuses the exact mass-property integration verified in the STEP → URDF converter (Eberly's polyhedral mass-properties method, exact to floating-point precision on an analytic cube) — here applied to meshes you already have, without needing the original CAD file.
Unit fixer: the classic "my robot exploded in simulation" bug is a mesh authored in millimetres loaded as if it were metres (or vice versa) — a 1000× mass/inertia error. This tab flags an implausible bounding box (very large or very small for a single robot link) and rescales + re-downloads the mesh. The threshold is a heuristic, not a certainty — always sanity-check the reported size yourself.
Next: paste the inertial block into your robot with the URDF validator, or see it articulate in the 3D viewer.