Megohmcentimeter

Megohm-centimeter, abbreviated as MΩ·cm, is a unit of electrical resistivity (volume resistivity) used for insulating materials. It expresses how much resistance a material would present to current flowing through a sample with unit cross-sectional area and unit length. The resistivity is denoted ρ, and the relationship to geometry is R = ρL/A for a sample of length L and cross-sectional area A. A useful conversion is 1 MΩ·cm = 10^6 Ω·cm = 10^4 Ω·m, so ρ in MΩ·cm can be converted to the SI unit ohm-meter by multiplying by 10^4.

The unit is widely used in materials science and electronics to characterize bulk insulating properties of substances such as polymers, glasses, ceramics, and protective coatings. Higher ρ values indicate lower electrical conductivity and lower leakage current. Measurements can span many orders of magnitude, reflecting the wide range of insulating materials and surface conditions.

Measurement details: resistivity is determined from resistance measurements on a sample with known geometry, using ρ = R A / L. Temperature and humidity influence results, so measurements are typically specified at a standard temperature (for example 20°C or 25°C) and controlled humidity. In practice, MΩ·cm is favored for expressing very high resistivities, while SI-compatible conversions to Ω·m are used for calculations requiring standard units.

Relation to conductivity: electrical conductivity is the reciprocal of resistivity, σ = 1/ρ, with appropriate unit conversions when using ρ in MΩ·cm.