How to Calibrate, Use, and Read an Ohmmeter

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Measure resistance & check the continuity of a circuit accurately
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An ohmmeter is an electronic device that measures resistance in an electronic component or circuit. It works by using 2 probes to send a current through the circuit and measuring how much resistance, in ohms (Ω), that current encounters. In this article, we’ll show you how to calibrate and use your ohmmeter (or multimeter) to test the resistance and continuity of an electrical circuit, plus explain the difference between an ohmmeter and multimeter.

How to Use and Read an Ohmmeter

Cut power to the circuit and disconnect the component. Plug the black lead into the “COM” port and the red lead into the ohms port. Touch the probes together to zero out the meter, then touch them to both sides of the component. A high value indicates high resistance. Adjust the ohm range if needed for a clear reading.

Section 1 of 4:

Calibrating Your Ohmmeter

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  1. Watermark wikiHow to Use an Ohmmeter
    On most ohmmeters, you will see a “common,” or negative plug (often labeled “COM”), and a “positive” plug. These may also be color-coded, with the black lead going into the negative (“COM”) plug and the red lead going into the positive plug. [1]
    • If you’re using a multimeter with more than 2 sockets, plug the black lead into the “COM” socket and the red lead into the socket designated for measuring resistance in ohms (usually marked with the ohms symbol, Ω). Set your multimeter to the ohms or continuity setting. [2]
    • Ohmmeters are typically sold along with these test leads. If your meter was recently purchased, you should not have to buy your leads separately.
    • Be sure to plug the short, bent ends (called banana jacks) of the leads into the sockets. The longer ends, with the grips and probes, are the ends you’ll use to actually test a circuit’s resistance.
    • Tip: Make sure your meter has a battery installed (or is plugged in). If you just bought an ohmmeter, the battery may have come pre-installed in your unit, or packaged separately with instructions for installing it.
  2. Watermark wikiHow to Use an Ohmmeter
    Master electrician Daniel Stoescu says, “Always check the ohmmeter functionality by touching the leads together before making any measurements.” [3] When you touch the probes together, the needle on an analog ohmmeter should point all the way to the right (indicating no resistance). If the needle or screen doesn’t do this, turn the adjustment knob on your ohmmeter until the needle reads 0 ohms when the probes are touching each other.
    • Note that the scale on analog meters reads in the reverse direction of most conventional measuring scales: less resistance is to the right and more resistance is to the left.
    • If yours is a digital ohmmeter , the screen should read “0” (or no more than “0.5”) when you touch the 2 probes together. [4]
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  3. Watermark wikiHow to Use an Ohmmeter
    Get a resistor (or several resistors) whose resistance is already known. Then, use your ohmmeter to measure the resistor’s resistance and see if you get the reading that you expect to. [5]
    • You can technically use anything that conducts electricity to test your ohmmeter, from a piece of aluminum foil to a pencil mark on a sheet of paper, as long as you know that object’s resistance value ahead of time. Place the meter’s probes on opposite ends of the conductor and look to see if the correct resistance reading shows up on the meter’s screen.
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Section 2 of 4:

Measuring Resistance with an Ohmmeter

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  1. Watermark wikiHow to Use an Ohmmeter
    Stoescu warns to “Never use an ohmmeter on live circuits.” [6] If you’re measuring the resistance inside a circuit or wire, it has to be completely dead in order for you to get an accurate reading. This is also very important for your own safety. [7]
    • Another source of power isn't necessary since your ohmmeter will supply all of the voltage and current for your circuit.
    • Trying to use an ohmmeter on a powered circuit can cause incorrect readings as well as damage to the meter, the circuit, and you.

    Warning : When testing an electronic circuit, be sure it is not live. This means not only unplugging it, but also discharging any capacitors in the circuit. Televisions and other electronics with cathode ray tubes and microwave ovens can have capacitors charged with thousands of volts even when unplugged.

  2. On some meters, you have the option to turn the dial in the center of your ohmmeter to change the scale of the reading, from tens, to hundreds, to thousands, and so on. For the best results, turn your meter to the lowest scale that is still higher than the resistance of what you’re measuring.
    • For example, if you expect the circuit you’re measuring to have a resistance of 1100 ohms, then your ohmmeter should be set to X100. This means, a reading of “11” on your ohmmeter would be equal to 1100 ohms.
    • Note that you can only do this if you have an idea of what the resistance of what you’re measuring ought to be.
  3. If you have an idea of how many ohms you’ll be measuring, select an appropriate range (for example, up to 6000.0 Ω or up to 60.00 MΩ) that encompasses that measurement. Typically, you’ll press the “Range” button on your meter until you find the setting you need. Most digital ohmmeters and multimeters have an auto-range function that will adjust for you. [8]
    • You’ll need to have an approximate idea of the resistance of the circuit you’re measuring if you’re setting the range yourself. Start with a high range and gradually reduce it if you’re unsure.
  4. Watermark wikiHow to Use an Ohmmeter
    Place 1 probe on 1 end of the circuit and place the other probe on the other end. Note that it doesn’t matter which probe is touched to which end of the circuit. [9]
    • Because you’re measuring the resistance in the circuit and resistance doesn’t change with the direction of current flow, the positive probe and the negative probe can be on either end of the circuit to get an accurate resistance reading.
  5. This number, multiplied by the scale that your meter is set to, is equal to the circuit’s resistance in ohms (Ω). The lower the resistance, the easier it is for electrical current to flow through the circuit. [10]
    • For example, if a circuit has 0 ohms, current would be able to flow through the circuit completely unimpeded.
  6. Watermark wikiHow to Use an Ohmmeter
    Remove the resistor you want to measure from the circuit board by unsoldering the pins using a soldering iron . This will ensure that you’re not getting an inaccurate reading through another path in the circuit. [11]
    • In other words, by testing a resistor while it’s still in a circuit board, you can’t be sure that the resistance you’re measuring is only coming from that particular resistor.
  7. Watermark wikiHow to Use an Ohmmeter
    Occasionally, the test leads will become shorted while the device is stored, draining the battery. The best way to prevent this is to turn off the ohmmeter and disconnect the wires before you store it.
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Section 3 of 4:

Checking Continuity with an Ohmmeter

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  1. In electrical terms, continuity is the presence of a direct path for electricity to flow between 2 points or through a circuit when closed. Most multimeters have a specific continuity setting, but you can also use a plain ohmmeter (or the ohms setting on a multimeter): [12]
    • Set your scale to the lowest setting.
    • Touch the ends of the probes to either end of the circuit or component you’re testing (just like if you were measuring resistance).
    • Look for a reading between “0” and “2” to indicate continuity. This means electricity is able to flow and the circuit is closed and working.
    • On digital ohmmeters and multimeters, an infinity symbol (∞) or “OL” (“open line”) result means there is not continuity and that the circuit is open or bad.
Section 4 of 4:

Ohmmeter vs. Multimeter

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  1. Multimeters look similar to ohmmeters, but with more sockets, buttons, and abilities. They measure resistance in ohms, just like an ohmmeter, but can also check for continuity and measure voltage in Volts (V) and current in amperes (A). [13] If you’re investing in a tool for general electrical work, a multimeter is more versatile than an ohmmeter and has all the same capabilities.
    • Both multimeters and ohmmeters can be digital or analog:
      • Analog meters are very basic and inexpensive and usually range from 0–10 to 0–10,000 ohms.
      • Digital meters may have similar ranges or “auto-range,” where the device will read a circuit’s resistance and automatically select the best measuring range.
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Expert Q&A

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  • Question
    What is the first thing to do when using the ohmmeter?
    Daniel Stoescu
    Master Electrician
    Daniel Stoescu is a Master Electrician and the Owner and Operator of Home Tech Solutions, LLC in Hampton, Virginia. With over a decade of experience, Daniel specializes in wiring residential, commercial, and light industrial structures. The Home Tech Solutions team has over four decades of combined experience and offers comprehensive solutions for residential electrical needs.
    Daniel Stoescu
    Master Electrician
    Expert Answer
    Before taking any measurements, make sure the ohmmeter works by touching the leads together.
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    Not Helpful 8 Helpful 12
  • Question
    Can you use an ohmmeter on a live circuit?
    Daniel Stoescu
    Master Electrician
    Daniel Stoescu is a Master Electrician and the Owner and Operator of Home Tech Solutions, LLC in Hampton, Virginia. With over a decade of experience, Daniel specializes in wiring residential, commercial, and light industrial structures. The Home Tech Solutions team has over four decades of combined experience and offers comprehensive solutions for residential electrical needs.
    Daniel Stoescu
    Master Electrician
    Expert Answer
    No, you can't. You should never use your ohmmeter to test any live circuits.
    Thanks! We're glad this was helpful.
    Thank you for your feedback.
    If wikiHow has helped you, please consider a small contribution to support us in helping more readers like you. We’re committed to providing the world with free how-to resources, and even $1 helps us in our mission. Support wikiHow
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    Not Helpful 1 Helpful 8
  • Question
    How do you use measured ohmmeter resistance directly?
    Community Answer
    You can use it by determining if a device is shorted or open. This type of test is called OUT-OF-THE -CIRCUIT test. Examples are: Testing a fuse, breaker, switch, filaments etc.
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      References

      1. ↑ https://www.sciencebuddies.org/science-fair-projects/references/how-to-use-a-multimeter
      2. ↑ https://circuitdigest.com/tutorial/how-to-test-if-multimeter-is-working-or-not
      3. ↑ Daniel Stoescu. Master Electrician. Expert Interview. 21 June 2021.
      4. ↑ https://circuitdigest.com/tutorial/how-to-test-if-multimeter-is-working-or-not
      5. ↑ https://circuitdigest.com/tutorial/how-to-test-if-multimeter-is-working-or-not
      6. ↑ Daniel Stoescu. Master Electrician. Expert Interview. 21 June 2021.
      7. ↑ https://ecampusontario.pressbooks.pub/multimeters101/chapter/1-6-introduction-to-resistance-measurements/
      8. ↑ https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-measure-resistance
      9. ↑ https://www.sciencing.com/use-ohmmeter-test-ac-transformer-7812347/
      1. ↑ https://www.sciencebuddies.org/science-fair-projects/references/how-to-use-a-multimeter
      2. ↑ https://www.sciencing.com/use-ohmmeter-test-ac-transformer-7812347/
      3. ↑ https://www.tigerstop.com/blog/how-to-test-a-fuse-with-an-ohmmeter/
      4. ↑ https://www.sciencebuddies.org/science-fair-projects/references/how-to-use-a-multimeter

      About This Article

      Article Summary X

      To use an ohmmeter, start by disconnecting all power to the circuit that you're testing. Next, turn the dial in the center of your ohmmeter to change the scale of the reading from tens, to hundreds, to thousands, and so on. Use the lowest scale available on the meter that is higher than the resistance of what you’re measuring. Then, touch the 2 probes to opposite ends of the circuit and read the number on the ohmmeter to find the circuit’s resistance. Keep in mind that the lower the resistance, the easier it is for current to flow through the circuit! For tips on setting up your ohmmeter properly, read on!

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