How to Use a Multimeter to Measure Voltage, Current and Resistance

Updated on December 5, 2017
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Eugene is a qualified control/instrumentation engineer Bsc (Eng) and has worked as a developer of electronics & software for SCADA systems.


What is a Multimeter?

A digital multimeter or DMM is a useful instrument for measuring voltage, current and resistance, and some meters have a facility for testing transistors and capacitors. You can also use it for checking continuity of wires and fuses. If you like to DIY, do car maintenance or troubleshoot electronic or electrical equipment, a multimeter is a handy accessory to have in your home toolkit.

If you have any questions, just leave a comment at the end of this "how to" guide. Also if you find this article useful, please share it on Facebook or other social media using the easy share buttons.


Volts, Amps, Ohms - What Does it All Mean?


This is the pressure in an electrical circuit


This is a measure of the current flowing in an electrical circuit


A measure of the resistance to flow in a circuit

Voltage Source

This produces a current flow in a circuit. It could be a battery, generator, mains supply or bench power supply


A device or component which draws power from a voltage source. This could be an electronic resistor, bulb, electric heater, motor or any electrical appliance


This is usually the point in a circuit to which the negative terminal of a battery or power supply is connected


Direct current. Current flows only one way from a DC source, an example of which is a battery


Alternating Current. Current flows one way from a source, reverses, and then flows the other way. This happens many times a second at a rate determined by the frequency which is typically 50 or 60 hertz. The mains supply in a home is AC

If you would like some more detailed information about these quantities, take a detour to this hub:

Volts, Watts, Amps, Kilowatt Hours, What Does it All Mean ? - The Basics of Electricity

Using a Multimeter - Measuring Functions on the Instrument

A basic multimeter facilitates the measurement of the following quantities:

  • DC voltage
  • DC current
  • AC voltage
  • Resistance
  • Continuity - indicated by a buzzer or tone

Some basic meters don't have an AC current range.

In addition meters may have the following functions:

  • Capacitance measurement
  • Transistor HFE or DC current gain
  • Temperature with an additional probe
  • Diode test
  • Frequency

Voltage, current and resistance ranges are usually selected by turning a rotary dial, and the measurement is indicated on an LCD display or scale. Laboratory bench DMMs sometimes have seven segment LED displays.

Typical multimeter or DMM
Typical multimeter or DMM | Source


Damaged probes and test leads are a hazard. Never use a damaged probe to measure mains voltages!

Exposed conductor of test lead
Exposed conductor of test lead | Source

Voltage, Current and Resistance Ranges


How to Measure Voltage

  1. Power off the circuity/wiring under test if there is a danger of shorting out closely spaced adjacent wires, terminals or other points which have differing voltages
  2. Plug the black ground probe lead into the COM socket on the meter (see photo below)
  3. Plug the red positive probe lead into the socket marked V (usually also marked with the Greek letter "omega" Ω and possibly a diode symbol)
  4. If the meter has has a manual range setting dial, turn this to select AC or DC volts and pick a range to give the required accuracy. So for instance measuring 12 volts on the 20 volt range will give more decimal places than on the 200 volt range.
    If the meter is autoranging, turn the dial to the 'V' setting with the symbol for AC or DC (see photo below)
  5. A multimeter must be connected in parallel in a circuit (see diagram below) in order to measure voltage. So this means the two test probes should be connected in parallel with the voltage source, load or any other two points across which voltage needs to be measured.
  6. Touch the black probe against the first point of the circuitry/wiring
  7. Power up the equipment
  8. Touch the other red probe against the second point of test. Ensure you don't bridge the gap between the point being tested and adjacent wiring, terminals or tracks on a PCB
  9. Take the reading on the LCD display

Note: A lead with a 4mm banana plug on one end and a crocodile clip on the other end is very handy. The croc clip can be connected to ground in the circuit, freeing up one of your hands


When measuring mains voltages, always turn off power before connecting measuring probes. If this isn't possible, connect to the neutral first.

WARNING !!! Safety First When Measuring Mains Voltages!

  1. Before using a meter to measure mains voltages, ensure the test leads aren't damaged and that there are no exposed conductors which could be touched inadvertently.
  2. Double check that the test leads are plugged into the common and voltage sockets of the DMM (see photo below) and not the current sockets. This is essential to avoid blowing up the meter.
  3. Set the range dial on the meter.
  4. Always turn off the power (if possible) before inserting the probes into a socket outlet, using the switch on the socket. Insert a probe into the neutral pin first before inserting a probe into the hot (live) pin of the socket. If you insert the probe into the hot (live) pin first and the meter is faulty, current could flow through the meter to the neutral probe. If you then inadvertently touch the probe, there is a possibility of shock.
  5. Finally turn on the power switch and measure the voltage.

If you are measuring voltage at a consumer unit/breaker box/fuse box, this video from Fluke Corporation outlines Safe practices when taking single phase measurements

Connecting Probe Leads to Measure Voltage

Test leads and 4mm sockets on a DMM, setup to measure voltage
Test leads and 4mm sockets on a DMM, setup to measure voltage | Source

Series and Parallel Connections

Explaining series and parallel connections (R1, R2 and R3 are resistors)
Explaining series and parallel connections (R1, R2 and R3 are resistors) | Source

Measuring Voltage - Meter in Parallel With Load

DMM connected in parallel with load to measure voltage across it
DMM connected in parallel with load to measure voltage across it | Source
A load could be an electronic resistor like this one, or an electrical appliance
A load could be an electronic resistor like this one, or an electrical appliance | Source

What Multimeter Symbols Mean?

Symbols used on an autoranging DMM
Symbols used on an autoranging DMM | Source

Autoranging Meters

Autoranging meters detect the voltage and select the range automatically to give the most amount of significant digits on the display. You must however set the mode to resistance, volts or current and also connect the probe lead to the proper socket when measuring current.

Fluke Multimeter with Auto-Ranging Facility

This autoranging multimeter from Fluke, a leading manufacturer of electronic test equipment, has an accuracy of 0.09% on DC ranges
This autoranging multimeter from Fluke, a leading manufacturer of electronic test equipment, has an accuracy of 0.09% on DC ranges | Source

What Multimeter Do I Need? - Buying a DMM

Fluke, who are a leading manufacturer of digital instrumentation, recommend the Fluke 113 model for general purpose use in the home or for car maintenance. This is an excellent meter and can measure AC and DC volts, current, resistance, check continuity and diodes. The meter is auto-ranging, so ranges don't have to be set. It is also a true-RMS meter

An alternative is the Fluke 177 model which is a high accuracy instrument (the specification is 0.09% accuracy on DC volts). A model like this is ideal for more accurate testing and professional use.

Fluke's multimeter recommendation
Fluke's multimeter recommendation | Source

How to Measure Current

  1. Turn off the power in the circuit being measured
  2. A multimeter must be inserted in series with the load in a circuit in order to measure current.
    Plug the ground probe into the COM socket and plug the red positive probe lead either into the mA socket or the high current socket which is usually marked 10A (some meters have a 20 A socket instead of 10A). The mA socket is often marked with the maximum current and if you estimate that the current will be greater than this value, you must use the 10 A socket, otherwise you will end up blowing a fuse in the meter
  3. Connect the meter in series as in the diagram below
  4. Turn the dial on the meter to the highest current range (or the 10A range if the probe is in the 10A socket). If the meter is autoranging, set it to the "A" or mA setting. (See the photo above for an explanation of symbols used).
  5. Turn on the power
  6. If the range is too high, you can switch to a lower range to get a more accurate reading
  7. Remember to return the positive probe to the V socket when finished measuring current. The meter is practically a short circuit when the lead is in the mA or 10 A socket. If you forget and connect the meter to a voltage source when the lead is in this position, you may end up blowing a fuse at best or blowing up the meter at worst! (On some meters the 10A range is un-fused)

Connecting Probe Leads to Measure Current

Test leads and sockets on a DMM, setup to measure current
Test leads and sockets on a DMM, setup to measure current | Source

Measuring Current - Meter in Series

DMM connected in series with load  to measure current
DMM connected in series with load to measure current | Source

Measuring Large Currents with a Clamp Meter

On most multimeters, the highest current range is 10 or 20 amps. It would be impractical to feed very high currents through a meter because normal 4 mm sockets and test leads wouldn't be capable of carrying high currents without overheating. Instead, clamp meters are used for these measurements.

Clamp meters (as the name suggests) have a spring loaded clamp like a giant clothes peg which clamps around a current carrying cable. The advantage of this is that a circuit doesn't have to broken to insert a meter in series, and power needn't be turned off as is the case when measuring current on a standard DMM. Clamp meters use either an integrated current transformer or hall effect sensor to measure the magnetic field produced by a flowing current. The meter can be a self contained instrument with an LCD which displays current, or alternatively the device can output a voltage signal via probe leads and 4mm "banana" plugs to a standard DMM. The voltage is proportional to the measured signal, typically 1mv represents 1 amp.
Clamp meters can measure hundreds or thousands of amps.
To use a current clamp, you simply clamp over a single cable. In the case of a power cord or multicore cable, you need to isolate one of the cores. If two cores carrying the same current but in opposite directions are enclosed within the jaws (which would be the situation if you clamp over a power cord), the magnetic fields due to the current flow would cancel out and the reading would be zero.

Fluke clamp meter
Fluke clamp meter | Source

How to Measure Resistance

  1. Turn off all power to the circuit being measured
  2. Disconnect one end of the resistance from the circuit. This may involve pulling off spade leads or desoldering a component. This is important as there may be other resistances in parallel with the resistance being measured
  3. The probes are connected to the meter in the same way as for measuring voltage
  4. Turn the dial to the lowest Ohm or Ω range. This is likely to be the 200 ohm range or similar
  5. Place a probe tip at each end of the resistance being measured
  6. If the display indicates "I", this means that resistance is greater than can be displayed on the range setting you have selected, so you must turn the dial to the next highest range. Repeat this until a value is displayed on the LCD

Connecting Probe Leads to Measure Resistance

Leads setup to measure resistance
Leads setup to measure resistance | Source

How to Check Continuity and Fuses

A multimeter is useful for checking breaks in flexes of appliances, blown filaments in bulbs and blown fuses, and tracing paths/tracks on PCBs

  1. Turn the selecting dial on the meter to the continuity range. This is often indicated by a symbol which looks like a series of arcs of a circle (See symbols used on meters below)
  2. The probes are connected to the meter in the same way as for measuring voltage
  3. If a conductor on a circuit board/ a wire in an appliance needs to be checked, make sure the device is powered down
  4. Place the tip of a probe at each end of the conductor or fuse which needs to be checked
  5. If resistance is less than about 30 ohms, the meter will indicate this by by a beep tone or buzzing sound. The resistance is usually indicated on the display also. If there is break in continuity in the device being tested, an overload indication, usually the digit "1", will be displayed on the meter.

Connecting Probe Leads to Check Diodes or Continuity

Leads setup to check diodes or continuity
Leads setup to check diodes or continuity | Source

How to Check Diodes

A multimeter can be used to check whether a diode is short circuited or open circuited. A diode is an electronic one way valve or check valve, which only conducts in one direction. A multimeter when connected to a working diode indicates the voltage across the component.

  1. Turn the dial of the meter to the diode test setting, which is indicated by a triangle with a bar at the end (see symbols used on meters below)
  2. The probes are connected to the meter in the same way as for measuring voltage
  3. Touch the tip of the negative probe to one end of the diode, and the tip of the positive probe to the other end
  4. When the black probe is in contact with the cathode of the diode (usually indicated by a bar marked on the component) and the red probe makes contact with the anode, the diode conducts, and the meter indicates the voltage. This should be about 0.6 volts for a silicon diode and about 0.2 volts for a Schottky diode. When the probes are reversed, the meter should indicate a "1" because the diode is open circuit and non-conducting.
  5. If the meter reads "1" when the probes are placed either way, the diode is likely to be faulty and open circuit. If the meter indicates a value close to zero, the diode is shorted circuited.
  6. If a component is in circuit, resistances in parallel will affect the reading and the meter may not indicate "1" but a value somewhat less

How to Measure Wattage and the Power Consumption of an Appliance With a Multimeter

Watts = Volts x Current

So to measure the power in watts of a load/appliance, both the voltage across the load and the current passing through it must be measured. If you have two DMMs, you can measure the voltage and current simultaneously. Alternatively measure the voltage first, and then disconnect the load so that the DMM can be inserted in series to measure current. When any quantity is measured, the measuring device has an influence on the measurement. So the resistance of the meter will reduce current slightly, and give a lower reading than the actual value with the meter not connected.

The safest way to measure the power consumption of an appliance powered from the mains is to use a power adapter. These devices plug into a socket and the appliance is then plugged into the adapter which displays information on an LCD. Typical parameters displayed are voltage, current, power, kwh, cost and how long the appliance was turned on (useful for fridges, freezers and air conditioners which cut in and out). You can read more about these gadget in my article here:

Checking Power Consumption of Appliances With an Energy Monitoring Adapter

An alternative way of safely measuring current drawn by an electrical appliance is to make up a test lead using a short piece of power cord with a trailing socket on one end and a mains plug on the other. The inner neutral core of the power cord could be freed and separated from the outer sheath, and current measured with a clamp meter or probe (Don't remove the insulation!) . Another way is to cut the neutral core, add 4mm banana plugs to each of the cut ends and plug these into the meter. Only make connections and adjust range on the meter with the power off!

Measuring watts = volts x amps
Measuring watts = volts x amps | Source
Power adapter. (Also known as an energy monitor/power tracker)
Power adapter. (Also known as an energy monitor/power tracker) | Source

How to Check Peak Voltages - Using a DVA Adapter

Some meters have a button which sets the meter to read max and min RMS voltages and/or peak voltages (of the waveform). An alternative is to use a DVA or Direct Voltage Adapter. Some components such as CDI (Capacitor Discharge Ignition) modules on vehicles and boats produce pulses which vary in frequency and can be short duration. A DVA adapter will sample and hold the peak value of the waveform so the component can be checked to see whether it's producing the correct voltage level. A DVA adapter typically has two probe leads as input for measuring voltage and either two output leads with banana plugs or a connector with fixed plugs attached for plugging into a meter with standard spaced sockets. The meter is set to a DC voltage range and the adapter typically outputs 1 volt DC per 1 volt AC input.

True RMS Multimeters

The voltage supply to your home is AC, and voltage and current vary in polarity over time. The waveform is sinusoidal as in the diagram below and the change in direction is either 50 or 60 times per second, depending on the country in which you live. The change in direction is known as the frequency and measured in Hertz. The RMS voltage of an AC waveform is the effective voltage and similar to the average voltage. If the peak voltage is Vpeak, then the RMS voltage for a sinusoidal voltage is Vpeak / √2 (approx 0.707 times the peak voltage). The power in a circuit is the RMS voltage multiplied by the RMS current flowing in a load. The voltage normally printed on appliances is the RMS voltage even though this is not usually stated.
A basic multimeter will indicate RMS voltages for sinusoidal voltage waveforms. The supply to our homes is sinusoidal so this isn't a problem. However if a voltage is non sinusoidal, e.g. a square or triangular wave, then the meter will not indicate the true RMS voltage. True RMS meters however are designed to correctly indicate RMS values for all shaped waveforms.

The AC Supply Feeding Our Homes is a Sine Wave

RMS and peak voltages of an AC sine waveform. Vpp is the peak to peak voltage
RMS and peak voltages of an AC sine waveform. Vpp is the peak to peak voltage | Source

Questions & Answers

    © 2012 Eugene Brennan


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      • eugbug profile image

        Eugene Brennan 3 weeks ago from Ireland

        Hi Jabba,

        The meter is practically a short circuit when the the leads are connected to measure current. If you connect it to a voltage source, it will blow the fuse in the meter. The high current range (10A/20A range) may not be fused on a cheap meter, so the meter will likely be destroyed if the voltage source can potentially supply a large current (the mains or a battery).

        Does this answer your question?

      • profile image

        jabba 3 weeks ago

        What is the consequence when testing (current) A and the probes are connected to (voltage) V?

      • profile image

        Loves chowri 2 months ago

        When you say the probe is in open air, are you holding it, or is it resting on a surface?....

      • profile image

        Tsegazeab 3 months ago

        How we measure the laptop voltage regulator

      • eugbug profile image

        Eugene Brennan 4 months ago from Ireland

        Hi Chris,

        I'm not an electrician, so I'm not going to advise what action should be taken in your specific case. It would be like a doctor diagnosing over the phone. However here are some thoughts and most of it is "do not do this at home" territory if you don't know what you are doing.:

        The figures you mention, are they volts or ma? Current will flow from neutral to ground through your meter if you touch one end to ground e.g. through water. The reason for this is that the supply transformer is grounded, so you are effectively making another path for the current to flow back to neutral at the transformer (neutral is connected to ground at the transformer). If the socket is wired incorrectly and hot and neutral are reversed, this can blow a fuse in the meter or blow it up.

        The system of ground rod, ground and pool could be acting effectively as a battery and electrochemical activity creating the voltages.

        Voltage could be coming from the plumbing feeding the pool via plumbing connections to other homes. This could be via the water and not necessarily metal plumbing. This is why it is important in homes, especially in bathrooms where we can be walking around in bare feet on wet floors and making good connection with ground, that all extraneous metal (metal you can touch under normal conditions of use, e.g. radiators, metal baths, drains, heated towel rails etc) is bonded or connected together so that there is no difference in potential.

        Here's some reading material which may be of use.

      • profile image

        Chris 4 months ago

        Nice article. My Dad is retired military. He had me check an outlet in my home by putting the black probe into the left side of a 3 prong outlet and the red probe in the toilet/sink water. He told me that my meter should read zero. It doesn't read zero. It reads 2.88 approx. The problem I have is coming from my pool. The pool is drawing between 2,88 and 3.90. I have had a couple of electricians come by and the power company. They checked the above ground transformers and said everything coming to the house is fine. The electricians shut all power in the house and the pool still reads the same voltage on the meter. It lightly shocked me/finger tingling the other day when I was standing outside the pool and touched the water at an area that I had a small cut on my finger. Anyway, My Dad had me go next door to the restaurant and do a similar meter test to their outlet and toilet. My meter read 5.30. Some have said my pool is grounded and it's stray current coming through ground. Others that I have talked with have never heard of this test that my Dad told me to do. I'm ultimately trying to stop the pool from shocking anyone. But I'm also trying to find information about the test my Dad had me do. I have a propane water heater not a traditional water heater and the house was built in 2006 on the beach. I would appreciate any help or thoughts about what you think might be going on. Thank you

      • eugbug profile image

        Eugene Brennan 4 months ago from Ireland

        Hi J,

        First check the meter reads 0 volts with the probes touched together to confirm there isn't a fault causing it to display an offset voltage.

        When you say the probe is in open air, are you holding it, or is it resting on a surface?

        A digital multimeter has a high impedance, typically 10 megaohms. When one probe is contacting a 220 volts supply and the other end is in free air, you effectively have a potential divider circuit. A potential divider (Google it for more details) consists of a number of resistors connected in series. When the divider is connected to a voltage supply, a reduced voltage is available at the junction between the resistors (an example is the volume control on a radio). In the most simplest of examples, two resistors of equal value will give half the input voltage at the junction. In your case, the meter forms one part of the potential divider. The other part consists of the resistance from probe through the air to ground (practically infinite), the resistance from the probe through your hand to ground (could be hundreds of megaohms if there is high humidity) and the reactance of the probe to ground (due to capacitance). The latter three are in parallel.

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        J. Karthikeyan 4 months ago

        Digital multimeter two probes. One probe places in phase 230VAC, another probe placed in open air. But meter reading shows 30V. Meter reading is correct? Pls explain.

      • profile image

        Don 8 months ago

        Verry informative information was a bit stale now remember many thanks kind regards Don

      • profile image

        Rochy/Scientist Sandy. 8 months ago

        Thank you very much for such helpful information, I'm passionate with electronics and inventing some cool devices, and my aim is to make free energy/electricity, so my problem is that I don't know how do we determine voltage a diode can handle like 1N4008 or 1N540 and Voltage regulator and transistor, my question is how do we determine their voltage rating because some of them are not even written or they're faded and where and in which circumstances do we use suppression capacitor, I'd like it if u poke me on my email when u get chance to answer my question and where to follow my answer thank you for your knowledge.

      • eugbug profile image

        Eugene Brennan 10 months ago from Ireland

        You can use a potential divider circuit to measure high voltages with a low voltage range meter. In fact this is how the internal circuitry in a meter reduces voltage for the various ranges. However the effort required isn't really worth it. You would also have to build everything into a box so that there are no wires/terminals/components exposed which could cause shock. You can buy a multimeter for about $10 from Dealextreme or other similar gadget suppliers which will measure voltage, current and resistance.

      • profile image

        TW 10 months ago

        How to use a low range voltmeter for high voltages

      • eugbug profile image

        Eugene Brennan 14 months ago from Ireland

        Hi Pascal,

        This won't damage the meter (assuming the voltage is less than the rating at the input sockets, typically 600 volts)

        An AC voltage is in effect DC for each half of a cycle, so DC is being applied to the inputs anyway.

        Remember when you are making a measurement with a meter to set the range first before you connect the probes to the voltage under test.

        When measuring current, a meter usually has two current sockets. The lower current socket is usually fused, but the higher current socket may or may not be fused. If you estimate the current being measured will be higher than the value indicated on the lower current socket, connect the probe to the higher current socket, otherwise you'll nd up blowing a fuse.

        Hope this helps!

      • profile image

        pascal 14 months ago

        hi I have a question suppose that I want to measure a DC voltage and I mistaken I point the rotary to AC . what will I do?

      • eugbug profile image

        Eugene Brennan 3 years ago from Ireland

        Hi "lost",

        by test leads being damaged, I mean any insulation scuffed, peeled back or cut to the extent that the inner copper cores are exposed and liable to be touched. Also insulation can crack, and leads pull out from the probe or plug end of the test lead, again exposing the conductor. I think I have a damaged set of leads, so I'll upload a photo.

        I'll add explanations with graphics of serial and parallel connections. Let me know if anything else needs explaining.

      • profile image

        lost 3 years ago

        Very Good info , can you explain what some of the things are for people like myself that are Very Very unfamiliar with the terminology ? In the safety first alone I was lost on leads not being damaged , (maybe a picture glossary of lingo) or what a series or parallel is etc. love this hub ,just from my lack of certain words or terms and their meaning I was lost from the start. Thank You

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