How to Use a Voltmeter

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Updated: March 29, 2019

Explore this Article Setting the Device Measuring Voltage Reading an Analog Voltmeter Article Summary Questions & Answers Related Articles References

A voltmeter is one of the most useful devices for home electrical testing, when used correctly. Before using a voltmeter for the first time, learn how to set the device correctly, and test it out on a low-voltage circuit such as a household battery.

This article describes how to test for voltage. You may also be interested in using a multimeter to test for current and resistance.

Part 1
Setting the Device

  1. 1
    Set your device to measure voltage. Most voltage-measuring devices are actually multimeters, which can test several aspects of electrical circuits. If your device has a knob with several settings, set it to one of the following:[1]
    • To test the voltage of an AC circuit, set the knob to V~, ACV, or VAC. Household circuits are almost always Alternating Current.
    • To test voltage of a DC circuit, choose V–, V---, DCV, or VDC. Batteries and portable electronics are typically Direct Current.
  2. 2
    Choose a range above the max expected voltage. Most voltmeters have several options marked for voltage, so you can change your meter's sensitivity to get a good measurement and avoid damaging the device. If your digital device has no range option, it is "autoranging" and should detect the correct range itself. Otherwise, follow these guidelines:
    • Choose a setting higher than the maximum expected voltage. If you have no idea what to expect, choose the highest setting to avoid damaging the device.
    • Household batteries are usually labeled with the voltage, typically 9V or below.
    • Car batteries should be at approximately 12.6V when fully charged with the engine off.[2]
    • Household outlets are typically 240 volts in most of the world, and 120 volts in the US and some other countries.[3]
    • mV stands for millivolt (1/1000 V), sometimes used to indicate the lowest setting.
  3. 3
    Insert the test leads. Your voltmeter should come with one black and one red test leads. Each has a metal probe on one end, and a metal jack on the other that slots into the holes in your voltmeter. Plug in the jacks as follows:[4]
    • The black jack always plugs into the hole labeled "COM."
    • When measuring voltage, plug the red jack into the hole labeled V (among other symbols). If there is no V, choose the hole with the lowest number, or mA.

Part 2
Measuring Voltage

  1. 1
    Hold the probes safely. Do not touch the metal probes while connecting them to a circuit. If the insulation looks worn or torn, wear electrically insulated gloves or purchase replacement leads.
    • The two metal probes should never touch each other while they are connected to a circuit, or severe sparking could result.
  2. 2
    Touch the black test lead to one part of the circuit. Test circuits for voltage by attaching the leads in parallel. In other words, you'll touch the probes to two points an already-closed circuit, with current running through it.
    • On a battery, touch the black lead to the negative terminal.
    • In a wall outlet, touch the black lead into the neutral hole, which in the US is the larger vertical hole, or the vertical hole on the left.[5]
    • Whenever possible, let go of the black test lead before moving on. Many black probes have a small plastic bump that can stick into an outlet.
  3. 3
    Touch the red test lead to another point on the circuit. This will complete the parallel circuit and cause the meter to display the voltage.
    • On a battery, touch the red lead to the positive terminal.
    • In a wall outlet, fit the red lead into the "hot" hole – in the US, this is the smaller, vertical or the vertical hole on the right.[6]
  4. 4
    Raise the range if you get an overload reading. Immediately raise the range to a higher voltage setting if you get one of the following results, before your device is damaged:
    • Your digital display reads "OL," "overload," or "1."[7] Note that "1V" is a real reading, and nothing to worry about.
    • Your analog needle shoots to the other side of the scale.
  5. 5
    Adjust the voltmeter if necessary. You may need to make adjustments if a digital voltmeter display reads 0V or nothing at all, or if an analog voltmeter's needle has barely moved. If there is still no reading, try the following in order:
    • Make sure the test probes are both connected to the circuit.
    • If you are measuring a DC circuit and get no result, look for a small knob or switch on your device labeled DC+ and DC- and move it to the other position.[8] If your device does not have this option, reverse the positions of the black and red probes.
    • Reduce the range by one setting. Repeat if necessary until you get a real reading.
  6. 6
    Read the voltmeter. A digital voltmeter will clearly display the voltage on its electronic screen. An analog voltmeter is a little more complicated, but not too tough once you learn the ropes. Continue reading for instructions.

Part 3
Reading an Analog Voltmeter

  1. 1
    Find a voltage scale on the needle's dial. Choose one that matches the setting you chose on your voltmeter's knob. If there is no exact match, read from a scale that's an easy multiple of the setting.
    • For example, if your voltmeter is set to DC 10V, look for a DC scale with a max reading of 10. If this isn't available, find one with a max of 50.
  2. 2
    Estimate the needle's position based on nearby numbers. This is a linear scale just like a ruler.
    • For instance, a needle pointing halfway between 30 and 40 indicates a reading of 35V.
  3. 3
    Divide your answer if using a different scale. Skip this step if you are reading from a scale that exactly matches your voltmeter's setting. Otherwise, correct for the difference by dividing the printed scale's max value by your knob setting. Divide the number the needle points to by your answer to get the actual voltage.
    • For example, if your voltmeter is set to 10V but you are reading off a 50V scale, calculate 50 ÷ 10 = 5. If the needle is pointing at 35V, your actual result is 35 ÷ 5 = 7V.

Community Q&A

Add New Question
  • Question
    Do I need to shut the power off before testing with a voltmeter?
    Community Answer
    No. You need power to test.
  • Question
    Can I check an extension cord with a voltmeter?
    Community Answer
    Yes, you can check the voltage by plugging in the cord, then setting your meter to ACV (AC Volts) on a scale higher than your line voltage. Or set the meter to the lowest resistance range, and measure each wire separately from plug to receptacle (not plugged in) -- should be 0 for each. The wide prong on plug should read to the wide slot on receptacle.
  • Question
    What is the use of a voltmeter?
    Community Answer
    To measure an electrical tension in volts.
  • Question
    What should I do to set meter for 24v check?
    Community Answer
    Determine AC or DC. Since it's sow low, I assume you are originally testing a battery, if so it's DC. Use 200 V DC to test.
  • Question
    What is a true RMS meter?
    Community Answer
    It is a tool that can measure alternating current. Most of these also come in multimeter form and thus can be used to measure current, voltage, and resistance all on a whim. They are incredibly useful for reading AC (alternating current) and may be useful for measuring DC (direct current).
  • Question
    What volt reading is full for a 6 volt battery?
    Community Answer
    6 volts is the maximum value it can output. It decreases over time and goes to a value not valid to operate the device it is inserted into. This is why toys can make sounds that decrease in pitch or even stop once the batteries reach a certain age.
  • Question
    How can I test for bad resistors on a circuit board?
    Community Answer
    First, turn off the power source of the circuit (if any) and isolate the "bad" resistors from the circuit board as it may yield to incorrect readings. Visually inspect the resistor and calculate its resistance and use the upper tolerance limit. Set your voltmeter/multimeter to an ohm range higher than your upper limit resistance (i.e. if your upper limit is 1,500 ohms, then your setting should be at 2,000 ohms) and then connect your test leads on the legs of the resistor. Lastly, compare your readings with your computation. If it's within the tolerance range, then it's good. Otherwise, it's bad.
  • Question
    Can I test an 8 volt battery with a volt meter?
    Community Answer
    Yes, you can, but why would you need to find the volts of a battery when you already know it is an 8 volt battery?
  • Question
    Is it okay to put a voltmeter in a socket?
    Community Answer
    No. You cannot do this with a direct current voltmeter at any point. Use an alternating current voltmeter instead, and do not stick anything into an electrical socket besides plugs.
  • Question
    Can I use the voltmeter as a battery charger?
    Community Answer
    No. A voltmeter detects the voltage that is in your battery. It does not charge it.
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    • The instructions for testing wall outlets assume you are trying to detect the voltage "seen" by the appliance you plug in. If you are trying to detect wiring problems, you may also wish to measure the voltage between the ground and one other hole. If you get a low result (say 2V), that hole is the neutral wire, and you've just measured the voltage drop. If you get a higher result (say 120V or 240V), that hole is attached to the hot wire.[9]


    • Improper use can destroy the device, cause a severe electrical shock, or create electrical sparking that can start a fire. These are much more likely to occur in a wall outlet or other high-voltage circuit than when testing a low-voltage battery.

    Article SummaryX

    To use a voltmeter, set the device to measure voltage and choose the type of electrical circuit you're working with. Next, select a range setting above the max expected voltage of the circuit. Then, insert the black test lead into the hole labeled "COM" and plug the red test lead into the hole labeled "V." Be careful not to touch the metal probes when you're connecting them to the circuit! If you get an overload reading, raise the range to a higher voltage setting and try again. For tips on using an analog voltmeter, read on!

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    Categories: Cabling and Wiring Connection

    In other languages:

    Español: utilizar un voltímetro, Italiano: Utilizzare un Tester, Deutsch: Ein Voltmeter benutzen, Français: utiliser un voltmètre, Русский: использовать вольтметр, Português: Usar um Voltímetro, Bahasa Indonesia: Menggunakan Voltmeter, Nederlands: Een voltmeter gebruiken, العربية: استخدام مقياس فرق جهد

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