mm⁴
millimeter to the fourth
Area moment of inertiaexact by definition
The millimetre to the fourth power is exactly 10⁻¹² m⁴, an exact relation. It is the consistent unit when working with dimensions in millimetres and stresses in N/mm², since a moment in N·mm divided by \(I\) in mm⁴ times a distance in mm gives a stress in N/mm² directly.
Watch out: Real sections give very large numbers in mm⁴: an IPE 300 is 83 600 000 mm⁴. European tables therefore print the same value as 8360 cm⁴, and some sources print it as 83.6 × 10⁶ mm⁴. All three are the same section, and mistaking a cm⁴ table entry for mm⁴ understates stiffness by a factor of 10 000.
| 1 mm⁴ | 1 mm⁴ |
Solvers that use area moment of inertia