Hello Alvient!
PLease refer to https://en.wikipedia.org/wiki/Darcy_(unit)
This is a measure of permeability called a Darcy, it isn't truely a measurement of area.
Regardless: 1 darcy is equivalent to 9.869233×10−13 m², or 1 mD is 9.869233×10−10 m²
Hope this helps!