A Guide to Multimeters and How to Use Them

Multimeters are a super-handy tool, and they are easier to use than you think. We'll show you how.

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The uses of a multimeter

A multimeter (also known as a volt-ohm-milliammeter / VOM) is a box of electronic circuitry that troubleshoots almost any kind of electrical wiring or device. Just dial the proper function and scale, touch the two test leads to the wiring or device in question, and check the meter reading. Depending on the setting, a multimeter can:

  • Tell what voltage is present
  • Detect a broken connection
  • Detect a lack of power
  • Detect a poor connection
  • Detect a faulty part

With all its numbers, dials, and switches, a multimeter can be pretty intimidating. But because they are inexpensive and have so many uses multimeters are very much worth a purchase for anyone who, even occasionally, finds themselves diagnosing faulty wiring or testing a battery.

Just getting started as an electrician? Read this story to find out what an industry vet wishes he would have known on his first day in the field.

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Multimeter terms

A good way to visualize electricity is to think of it like a river. In a river, there’s a certain volume of water (similar to electrical amperage, or amps) flowing with a certain potential force (voltage) that encounters obstructions as it flows (resistance, measured in ohms). Hold that big picture in your mind, then add these key concepts:

  • Alternating current (AC) voltage: The type of electricity that powers your house.
  • Direct current (DC) voltage: The type found in auto and household batteries.
  • Resistance (measured in ohms): The lower the reading, the easier electrical current (measured in amps) flows through circuit material.
  • An open circuit equals trouble: There is high resistance from a broken connection, a faulty part or a switch that’s been turned off. There isn’t a complete circuit path and no current will flow.
  • A closed circuit is good: It means a minimum of resistance is present because a connection or part is working.
  • Continuity testing determines if an open or closed circuit exists in an appliance, electrical or electronic device and is a common use for multimeters.
  • On a multimeter, infinity signifies an open circuit. On an analog multimeter, infinity shows up as an unwavering needle that won’t move off the far left side on the display. On a digital multimeter, infinity reads “0.L.”
  • On a multimeter, “zero” means a closed circuit has been detected. The display needle moves to the far right side of an analog scale; “zero” reads “0.00” on a digital multimeter.
  • Selecting the proper range is very important and refers to setting the function switch on your multimeter to a voltage or amperage value that’s higher than the top value you anticipate testing. Digital multimeters have a nifty feature, auto-ranging, that automatically selects the widest possible range once you set the function switch for ohms, current and voltage (AC or DC). Auto-ranging gives you the safest testing capacity each time you change back and forth from, say, measuring resistance to voltage reading.

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How to use a multimeter

Step One: Decide what to test for

Both analog and digital multimeters require you to decide which to test for first: ohms, voltage or current.

Step Two: Select a range

Next, select the range you’ll be testing. For example, if you were to test AC voltage in a 120-volt wall outlet on an analog multimeter, but only set the function switch to 30 AC volts, you’d get a faulty reading. Instead, select a setting greater than 120 AC volts.

Step Three: Contact a circuit

Multimeters come with two colored test leads that connect to ports in the meter. The leads have electrically insulated handles with metal tips, called "probes". The black test lead is always plugged into the black port on the meter, labeled "COM". The red lead is plugged into one of the other ports, depending on which type of test is being performed. When the test probes contact a circuit, the findings are displayed on the LCD readout or analog meter scale.

For resistance (ohms) and continuity tests, batteries inside the VOM send a weak current through the circuit being tested to get the reading.  Before running a resistance test, avoid possible injury and damage to the multimeter by disconnecting power to appliances and shutting off circuits.

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Good techniques for using a multimeter

  • When testing DC voltage or amps, match the polarity of the probes to the “+” and “-” terminals of the DC source being measured. Matching polarity isn’t necessary for testing either AC voltage or amps, or for continuity or resistance readings.
  • For the most accurate readings, hold the probe tip points (not the sides) tightly to a contact. Avoid touching the metal tips with your fingers while testing. Your body could act as a circuit and influence a reading (and get you zapped!).
  • Each time you do an ohms test using an analog multimeter, touch the two probes together and use the calibration dial to “zero it out.” For a digital multimeter, touch the probes together and it automatically calibrates itself.

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What's the difference between digital and analog multimeters?

For appliance and electronic repairs, buy a digital (not analog) multimeter. A digital meter is much simpler to read, and you can change the functions on it more easily. Digital multimeters have LCD readouts, do continuity testing, and cost as little as $15. Some digital multimeters also feature auto-ranging and overload protection, as well as some other advantages analog multimeters lack.

Analog multimeters have multiple scales on the dial, a moving needle and many manual settings on the function switch. It’s tricky spotting the correct scale to read on the dial, plus you sometimes have to multiply the reading by 10 or 100 to get your final value. Depending on features (make sure it can do continuity testing), prices start at about $10.

For easier, hands-free viewing, choose a multimeter with a stand that will prop it up or hang it on a wall. If a multimeter doesn’t come equipped with either jumper wires or alligator clips (both about $4 each), buy them. Alligator clips are often used to firmly grip wiring or contacts for hands-free safe and accurate readings. Both types of multimeters and these accessories can be purchased at electronics stores, home centers and hardware stores.

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How to safely use a multimeter

VOMs are tools that an impulsive and foolish person should avoid. When it comes to electricity, a little knowledge is a dangerous thing. Read the manual on your meter before you begin. Touching contacts to live wires or equipment with the VOM dialed in to the wrong settings can is dangerous and could instantly fry your meter. Also, make sure the test leads are in good shape. If you see any cuts or cracks in the insulation, toss them out and buy new ones.

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How to test battery life with a multimeter

RED TEST LEAD JACK: VΩ

FUNCTION SETTING: Direct current (DC) voltage

SCALE SETTING: 12 volts (or auto if available)

TEST PROBES: Match the polarity (“+” to “+” and “-” to “-”) of the test probes and the battery.

GOOD READING: This car battery should be producing at least 12.6 volts. This ones a dud.

BAD READING: A fully charged battery with voltage readings 15 percent below their original rating should be replaced.

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How to check an electrical circuit with a multimeter

RED TEST LEAD JACK: VΩ

FUNCTION SETTING: Alternating Current

SCALE SETTING: Next setting higher than 120 volts (or auto if available)

TEST PROBES: Insert probes into the two side-by-side receptacle slots (doesn't matter which goes in which)

GOOD READING: 115 to 125 volts

BAD READING: Anything other than 115 to 125 volts

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How to check for a broken wire with a multimeter

RED TEST LEAD JACK: 

FUNCTION SETTING: Ω

SCALE SETTING: X-1k (or auto ranging if available)

TEST PROBES: Connect the prongs together at one end of the cord with a jumper wire, creating a closed circuit. Insert the testing probes in the other end to complete the circuit, and then turn on the multimeter. Don’t forget a second test to check along the safety ground wire too.

GOOD READING: A “0.00” reading would indicate “zero”—a closed circuit.

BAD READING: This “0.L.” reading indicates “infinity”—an open circuit. This cord has a broken wire or loose connection.

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How to test a wall switch with a multimeter

How to test a wall switch with a multimeter

Test whether this wall switch is bad. First, SHUT OFF THE POWER to the main electrical panel. Then disconnect one terminal wire—so you don’t measure the entire circuit a switch is tied into—and turn the switch “on” to test for a short circuit inside the switch.

RED TEST LEAD JACK:VΩ

FUNCTION SETTING: Ω

SCALE SETTING: X-1k (or auto ranging if available)

TEST PROBES: Hold them steady on the terminals. You don’t have to match the polarity.

GOOD READING: With the switch in the "on" position, a “zero” reading would indicate a closed circuit, a good switch.

BAD READING: With the switch in the "on" position, the needle reads “infinity”—an open circuit. The wall switch is bad.