mm⁻¹
per millimeter
Wavenumberexact by definition
The reciprocal millimetre is 10³ m⁻¹. It is the unit of spatial frequency in imaging and of grating rulings, and it is the natural unit whenever a periodic structure has a pitch measured in millimetres or fractions of one.
| 1 mm⁻¹ | 1,000 m⁻¹ |