From To S/m mS/m S/cm S/mm
S/m 1 1000 0.01 0.001
mS/m 0.001 1 1e-05 1e-06
S/cm 100 100000 1 0.1
S/mm 1000 1e+06 10 1

Each cell shows the factor to convert 1 unit of the row header into the column header.

Highlighted diagonal cells represent identity conversions (1:1).