You can measure outlet voltage safely with a digital multimeter in about 30 seconds

A multimeter is a handheld tool that measures electrical current, voltage, and resistance. To check an outlet's voltage, you set the dial to the AC voltage setting (marked V with a wavy line), insert the red probe into the outlet's hot slot (the smaller opening on the right), touch the black probe to the neutral slot (the larger opening on the left), and read the number on the screen. A standard US outlet should show between 110 and 120 volts. If it reads significantly lower or higher, or shows zero, something is wrong with that outlet or the circuit it's on.

This is a straightforward task that takes no special training, but the steps matter — doing them in the wrong order or using the wrong setting can give you a false reading or damage your meter. The good news is that multimeters are cheap (under $15 for a basic model), and once you know how, you can troubleshoot outlets, chargers, and power strips without calling an electrician for every question.

Key Takeaways

  • A digital multimeter with an AC voltage setting is the standard tool for checking outlet voltage safely.
  • Set the dial to AC voltage (V with a wavy line), not DC voltage, or your reading will be wrong.
  • Insert the red probe into the smaller right slot and the black probe into the larger left slot to measure correctly.
  • A healthy US outlet reads between 110 and 120 volts; readings below 100 or above 125 suggest a problem with the outlet or circuit.
  • If an outlet reads zero or very low voltage, do not plug in sensitive devices like computers until an electrician checks it.

What a multimeter is and why you need the right one

A multimeter is a single tool that measures three things: voltage (how much electrical pressure is in a wire), current (how much electricity is flowing), and resistance (how much a material blocks electricity). You do not need all three functions to check an outlet — you only need the voltage measurement — but buying a meter that does all three costs almost the same as buying one that does just voltage, so most people buy a full multimeter.

You need a digital multimeter, not an analog one (the old kind with a needle that swings across a dial). Digital meters are easier to read, cheaper, and less likely to give you a wrong answer. Look for one labeled "digital multimeter" or "DMM" at any hardware store, home improvement store, or online. A basic model costs $10 to $20 and will last for years.

The meter should have a dial with different settings, a digital display screen, and two probes — one red and one black — attached by wires. If the probes are not attached, they come in the box and plug into the meter. The red probe always goes into the hole marked with a plus sign or the word "V" (for voltage); the black probe goes into the hole marked with a minus sign or "COM" (for common ground).

Setting the dial to AC voltage before you start

The dial on your multimeter has many settings, and using the wrong one will either give you a false reading or show nothing at all. You need the AC voltage setting, which is marked with a "V" and a wavy line (≈) next to it. AC stands for "alternating current," which is what comes out of the outlets in your home. Do not use the DC voltage setting (marked V with a straight line and dashes), which is for batteries and electronics inside devices.

Most multimeters have multiple AC voltage ranges — you might see 200V, 600V, or 750V marked on the dial. For a standard US outlet, any of these ranges will work, but if your meter has a 200V setting, start there because it gives you a more precise reading. If the display shows "1" or "OL" (which means "overload"), the range is too low; turn the dial to the next higher voltage setting and try again.

Before you touch the outlet, double-check that the red probe is plugged into the V hole and the black probe is plugged into the COM hole. This takes five seconds and prevents you from getting a wrong reading or damaging the meter.

Inserting the probes into the outlet correctly

A standard US outlet has three holes: two vertical slots and one round hole below them. The two vertical slots are what you measure. The right slot (smaller) is the "hot" wire, which carries the electrical current. The left slot (larger) is the "neutral" wire, which completes the circuit. The round hole below is the ground, which you do not need to touch for a voltage check.

Hold the multimeter in one hand and the probes in the other. Insert the red probe into the right slot (the smaller one) and the black probe into the left slot (the larger one). Push them in straight, not at an angle, until they are fully seated. You should feel a slight resistance, but they should go in smoothly. If they do not fit or feel stuck, stop and check that you are using the right holes.

Keep both probes in the outlet for a few seconds while you read the display. The number that appears is the voltage. Once you have your reading, remove both probes at the same time by pulling straight out. Do not twist or wiggle them.

Reading the voltage number and what it means

The display on your multimeter will show a number, usually between 0 and 130 if you are measuring a US outlet. A healthy outlet reads between 110 and 120 volts. This range is normal and means the outlet is working correctly. Readings of 118V or 115V are both fine.

If the reading is below 100 volts — say, 95V or 85V — the outlet is not delivering full power. This can happen if the circuit is overloaded, the breaker is failing, or there is a loose connection somewhere in the wiring. Devices that need steady power, like computers or refrigerators, may not work reliably on a low-voltage outlet. If the reading is above 125 volts — say, 130V or 135V — the outlet is delivering too much power, which can damage sensitive electronics over time. Either situation warrants a call to an electrician.

If the display shows 0V or nothing at all, the outlet is dead. This usually means the breaker for that circuit has tripped, the outlet itself is broken, or there is a wiring problem. Try plugging a lamp into the outlet to confirm it is truly dead before assuming the meter is wrong.

Checking multiple outlets and understanding what varies

Voltage can vary slightly from outlet to outlet in your home, and it can also vary by time of day depending on how much power your neighborhood is using. If you check the same outlet at different times, you might see 118V one time and 116V another time. This variation is normal and not a sign of a problem.

If you are troubleshooting a specific problem — a device that keeps shutting off, a charger that is not working, or an outlet that feels warm — check the voltage at that outlet and also at an outlet on a different circuit (usually a different room or a different wall). If one outlet reads low and others read normal, the problem is likely with that specific outlet or its circuit. If all outlets in your home read low, the problem may be with your service from the power company, and you should contact them.

Keep in mind that checking voltage tells you whether power is reaching the outlet, but it does not tell you whether the outlet is wired correctly or whether the ground is working. If you suspect a wiring problem or want to test the ground, you need a more advanced test that a may have access to electrician can perform.

When to stop and call an electrician instead

Checking outlet voltage with a multimeter is safe as long as you follow the steps — the voltage in a standard outlet is not strong enough to hurt you if you touch the probes. However, there are situations where you should not try to troubleshoot on your own and should call an electrician instead.

Do not use an outlet that reads zero volts to plug in computers, medical devices, or anything else important until an electrician has checked it. Do not plug anything into an outlet that feels warm, smells like burning plastic, or has scorch marks around it, even if the voltage reads normal — these are signs of a fire hazard. If you check an outlet and the voltage is wildly high (above 140V) or wildly low (below 90V), do not use that outlet and call an electrician. If you are not comfortable inserting the probes into an outlet, or if your multimeter is not working the way you expect, there is no shame in asking a professional to do it instead.

Frequently Asked Questions

Can I check outlet voltage without a multimeter?

Not reliably. A plug-in outlet tester (a small device with lights that you plug directly into the outlet) can tell you whether an outlet is wired correctly, but it cannot measure the actual voltage. If you need to know the voltage number, you need a multimeter.

What if the outlet has two round holes instead of slots?

That is a two-prong outlet, which is older and less common in modern homes. The two holes are the hot and neutral wires. Insert the red probe into one hole and the black probe into the other. If you get a reading of 0V, try swapping the probes — you may have them in the wrong holes.

Is it dangerous to check outlet voltage?

No. The voltage in a standard US outlet (110–120V) is not strong enough to cause injury if you touch the probes. The danger comes from higher voltages (like in a breaker panel or power lines) or from water near electricity. As long as your hands are dry and you are not touching the metal tips of the probes, you are safe.

Why does my outlet read 120V one time and 115V another time?

Voltage naturally fluctuates throughout the day as the power grid's demand changes. Readings between 110V and 120V are all normal. If the voltage swings outside this range regularly, or if it is consistently below 110V or above 120V, that suggests a problem worth investigating.

Can I use a multimeter to check if a power cord is damaged?

Yes. Set the meter to the resistance setting (marked with the omega symbol Ω), touch one probe to each end of the cord, and the meter should show a very low number (close to 0). If it shows a high number or "OL," the cord is broken inside and should not be used.