Conductivity

Prof. Dr. Thorsten Jungmann (last updated 2025-09-03)

Conductivity (German: Leitfähigkeit, also Konduktivität or EC-Wert) describes the ability of a material to conduct electric current. It is also referred to as EC value (electrical conductivity). It is the reciprocal of resistivity.

Tensor quantity in a homogeneous field with homogeneous material → scalar quantity

This is a tensor quantity. By convention, however, this script treats it as a scalar quantity in the context of the homogeneous field and on the assumption of homogeneous material (for a detailed justification).

1 Quantity symbol and unit

The quantity symbol of conductivity is the Greek lower-case letter $\sigma$ (‘sigma’). Alternatively, you will also find the Greek lower-case letters $\kappa$ (‘kappa’) or $\gamma$ (‘gamma’) as the quantity symbol of conductivity. In this script, I use $\sigma$ in line with the SI.

2 Practical and worked examples

Calculating the conductance $G$ of a conductor:

$$G=\sigma \cdot \frac{A}{l}$$

where:

• $\sigma$ is the conductivity
• $l$ is the effective length of the conductor (add the outgoing and return conductors if necessary)
• $A$ is the cross-section of the conductor

3 Typical orders of magnitude

This is a material property that you can look up in the book of tables, for example. The following values are the basis for this script. Unless stated otherwise, they apply to high-purity materials at room temperature ($T=20°C$) and atmospheric pressure ($p=1013\mathrm{hPa}$).

Very good conductors

• Silver (Ag): $\sigma \approx 63\cdot 10^{6}S/m$
• Copper (Cu): $\sigma \approx 59\cdot 10^{6}S/m$
• Gold (Au): $\sigma \approx 42\cdot 10^{6}S/m$
• Aluminium (Al): $\sigma \approx 36\cdot 10^{6}S/m$

4 Example phrasings

• ‘The conductivity of copper is 59 megasiemens per metre.’
• ‘At 63 megasiemens per metre, silver has a better conductivity than copper, but it is considerably more expensive.’

5 Related quantities

• resistivity

6 Relevant components

• conductor, electric line, cable