How to Measure Resistance


How to Measure Resistance

Resistance is the measure of difficulty electrons have in flowing through a particular object. It is similar to the friction an object experiences when moving or being moved across a surface. Resistance is measured in ohms; 1 ohm is equal to 1 joule per second or 1 volt of electrical difference per 1 ampere of current. Resistance can be measured with an analog or digital multimeter or ohmmeter. Use the following steps to measure resistance to electric current.

Method 1 of 2: Testing Resistance With a Multimeter

1- Choose the item whose resistance you wish to measure.


2. Plug the probes into the correct test sockets. 

A multimeter often has multiple testing sockets, according to whether it is being used to test for resistance, voltage, or amperage (current). Usually the right sockets to test for resistance are one labeled “COM” (for common) and one labeled with the Greek letter omega, which is the abbreviation for “ohm.”

3- Turn on the multimeter.


4- Select the best testing range.

 This is usually close to the maximum testing range for the multimeter, but just under it. If your reading appears near 0, you’ll have to dial the range down.

  • If you are testing resistance with an analog multimeter, you must zero the meter before performing the actual test. Touch the probes to each other to create a short circuit, then adjust the controls to read 0 ohms. Digital multimeters do not need to be zeroed out.
  • Some digital multimeters will adjust the range for you automatically.



5- Touch the multimeter probes to the item you wish to measure.

 You may need to adjust the multimeter’s range downward to get a suitable reading.

  • If you change the range on an analog multimeter, you’ll have to zero it out again before touching the probes to the object to be measured under the new range setting.


6- Set the multimeter to a high voltage range after finishing the test.

 This will prevent the multimeter from being damaged if you use it in a subsequent test without adjusting it first.




7- Turn off the multimeter.

 This keeps the batteries from being drained when the multimeter is not in use.


Method 2 of 2: Ensuring a Good Test



1- Test resistance on components not in a circuit.

 Measuring resistance on a component in a circuit will cause inaccurate readings because the multimeter is also measuring resistance from the other components in a circuit as well as the one being tested. Sometimes, however, it is necessary to test resistance on components in circuit.

2- Test only components that are powered off.

 Current flowing through a circuit will cause inaccurate readings, as the increased current will create a higher resistance. Also, the additional voltage could damage the multimeter. (For this reason, testing the resistance of a battery is not advised.)



3- Check for diodes in the circuit.

 Diodes conduct electricity in only 1 direction; thus, reversing the position of the multimeter’s probes in a circuit with diodes will cause different readings.