mm⁻³
per cubic millimeter
Number densityexact by definition
The per cubic millimetre is exactly 10⁹ m⁻³, identical in value to per microlitre because a cubic millimetre is a microlitre. Older haematology and cerebrospinal fluid reports use it, and the identity is why a CSF white cell count of 5/mm³ and 5/μL are the same result.
| 1 mm⁻³ | 1,000,000,000 m⁻³ |