How to Calculate Volume Resistivity

Copper wire conducts well but still has resistance.

Even the most conductive wires have some level of resistance. Resistance is a function of volume, therefore resistance increases linearly with size. This measure is predominantly associated with conductive wires, though it also applies to other objects as well. Fuel tank sending units, for example, can measure the resistivity of the gasoline in a tank and send a reading to the gauge without ever using moving parts to obtain the reading.

Things You'll Need

• Calculator
• Ruler
• Ohmmeter

Instructions

1. Measure the area of the cross section of the material you have. If it is cylindrical, multiply pi by the square of the radius.

2. Measure the length of the material. Keep the same units you used to calculate the cross section. For example, if your cross section is measured in square centimeters, measure the length in centimeters.

3. Measure the resistance of the material with an ohmmeter. Attach the two leads to the material and turn the meter on. The meter will give you a result in ohms.

4. Multiply the resistivity of the material by the cross sectional area, then divide by the length. This will give you the volume resistivity of the material in length-ohms. For example, a copper wire with a resistivity of 0.025 ohms 10 cm in length and 1/4 cm in diameter will have a volume resistivity of (.25^2)(3.14)(0.025)/10 = 0.00049 cm-ohms.

References

• Calc Tool: Volume Resistivity Calculator
• Cirris: Continuity Test Resistance Calculator