Whats the resistivity of copper?

Resistivity allows us to compare different conductors' abilities to transmit electric current that is independent of the physical dimensions of the conductors.

Resistivity is defined as 'the resistance of a unit length of a substance with a uniform cross-section'. In SI, the unit of measurement of resistivity is the ohm metre; in US customary units, it is expressed in ohm circular mil per foot.

So, to finally answer your question, the resistivity of copper is 17.5x10-9 ohm metres at 20oC. To find the resistance of a copper conductor, you can then use the equation:

resistance = resistivity x (area / length)

Additional Answer

The resistivity of copper depends on the temperature it which it is measured. At 25°C, it is about 17 nΩ.m, or 1.7 µΩ.cm.

The resistance of a conductor is then p * L / A, where p is the above number.

So for a wire with a length of 1 m (i.e. 100 cm), and a cross sectional area of 2 cm², the resistance is 17e-6 * 100 / 2 = 85 µΩ