megaohm centimeter
Electrical resistivityexact by definition
The megaohm centimetre is one million ohm centimetres, exactly 1e4 ohm metres. It is the standard purity unit for high-purity water, where 18.2 MΩ·cm at 25 degrees Celsius is the theoretical maximum set by water's own self-ionisation and the number every polishing loop is designed to hold. The conversion is exact.
Watch out: Resistivity in megaohm centimetres and conductivity in microsiemens per centimetre are reciprocals of the same measurement, so 18.2 MΩ·cm is 0.055 μS/cm. Both are strongly temperature dependent and are reported compensated to 25 degrees Celsius. Neither says anything about dissolved gases, organics or particles, which is why semiconductor-grade water is specified on total organic carbon and particle count as well.
| 1 MΩ·cm | 10,000 Ω·m |