Resistivity

Resistivity (ρ) is a measure of how easily a material conducts electricity, it is defined as the product of resistance and cross-sectional area, divided by the length of the material. Resistivity will give the value of resistance through a material of length 1m and cross-sectional area 1m² which is useful when you need to compare materials even though they may not be the same size, however resistivity is also dependent on environmental factors, such as temperature.

Where R is the resistance, A is the cross-sectional area and l is the length.

You can rearrange the above equation to get a formula for the resistance of an object, given its dimensions and the resistivity of the material it is made from:

Where ρ is the resistivity, A is the cross-sectional area and l is the length.