What outlet voltage actually is, and why you might need to check it
Outlet voltage is the electrical pressure flowing through a wall socket — measured in volts. In the United States, standard household outlets deliver 120 volts. Some outlets, usually for large appliances like electric dryers or ovens, deliver 240 volts. If an outlet is damaged, wired incorrectly, or the circuit breaker is failing, it may deliver too little voltage, and your device won't work properly or at all.
You check outlet voltage with a tool called a multimeter — a handheld device that measures electrical current, resistance, and voltage. A basic multimeter costs $10 to $30 at any hardware store. You don't need an expensive one for this task. The reading takes about 30 seconds and tells you whether an outlet is delivering the right amount of power.
This is useful if a lamp won't turn on, a phone charger isn't working, or you're troubleshooting why a room feels like it has no power. It's also the first step before calling an electrician, because it tells you whether the problem is the outlet itself or the device you're plugging in.
Key Takeaways
- A multimeter is a $10 to $30 handheld tool that measures voltage in seconds and works on any outlet in your home.
- Set the multimeter dial to the AC voltage setting (marked with a V and a wavy line) before you touch any outlet.
- Insert the black probe into the neutral slot (the larger hole on the right) and the red probe into the hot slot (the smaller hole on the left) to get a reading.
- A healthy 120-volt outlet reads between 110 and 125 volts; a 240-volt outlet reads between 220 and 250 volts.
- If the reading is far outside that range or shows zero, the outlet is not working correctly and you should not plug in expensive devices until it is repaired.
How to set up your multimeter
Before you touch any outlet, prepare the multimeter. Remove it from the package and look at the dial on the front. You'll see different settings marked around the edge — some with V symbols, some with Ω (ohm) symbols, and some with A symbols. You need the AC voltage setting, which is marked with a V and a wavy line next to it (not a straight line, which is DC voltage).
Turn the dial to that AC voltage setting. Most multimeters have a range marked next to it — often 200V or 750V. Either one works for household outlets. If your multimeter has an auto-range feature (usually a button labeled "Auto" or "Range"), you can leave it on auto and the meter will pick the right range itself.
Once the dial is set, look at the two probes — the long wires attached to the meter. One is black and one is red. These are your contact points. The black probe is neutral (ground), and the red probe is hot (the live wire). Keep them separate until you're ready to use them.
Where to insert the probes and what the holes mean
Look at a standard 120-volt outlet. You'll see two vertical slots. The slot on the right is slightly larger than the slot on the left. The larger slot on the right is the neutral slot — this is where the black probe goes. The smaller slot on the left is the hot slot — this is where the red probe goes. This matters because it ensures you're measuring the voltage correctly.
Some outlets also have a round hole below the two slots. That's the ground hole and you don't need it for a voltage check. Ignore it.
For a 240-volt outlet (the kind used for dryers or ovens), the slots look different — they're usually at angles or one is U-shaped. The same rule applies: insert the black probe into one slot and the red probe into the other. If you're not sure which is which on a 240-volt outlet, insert the probes and take a reading. If the number is negative, you've reversed them — just flip them and take another reading. The absolute number is what matters.
Reading the voltage and what the numbers mean
Once both probes are inserted, look at the display on the multimeter. You'll see a number appear. For a standard 120-volt outlet, the reading should be between 110 and 125 volts. For a 240-volt outlet, it should be between 220 and 250 volts. These ranges account for normal fluctuations in your home's electrical system throughout the day.
If the reading is within those ranges, the outlet is working correctly. If it's significantly lower — say, 100 volts on a 120-volt outlet — the outlet is delivering power but at reduced voltage, which can cause devices to work slowly or not at all. If the reading is zero or shows no number, the outlet has no power flowing through it at all.
Write down the reading or take a photo of the display. If you're checking multiple outlets, this helps you spot patterns — for example, if all outlets on one wall are low, it might be a circuit breaker issue rather than individual outlets failing.
What to do if the voltage is wrong
If an outlet reads significantly lower than it should, first check whether anything else on that circuit is drawing power. Unplug other devices from nearby outlets on the same circuit, wait 30 seconds, and check the outlet again. Sometimes a heavy load elsewhere causes a temporary voltage drop.
If the voltage is still low, the problem is likely in the outlet itself, the wiring behind the wall, or the circuit breaker. Do not plug expensive devices into that outlet — a phone charger or lamp is fine, but avoid plugging in a computer, television, or refrigerator until the outlet is checked by an electrician. Low voltage can damage electronics over time.
If the reading is zero, the outlet has no power. Check the circuit breaker panel in your home (usually in a basement, garage, or utility closet). Look for a breaker switch that is in the middle position or flipped to the off side. If you find one, flip it all the way off, then flip it back on. This resets the breaker. Check the outlet again. If it still reads zero, contact an electrician.
Safety reminders when using a multimeter
A multimeter is safe to use on household outlets because you're only measuring voltage, not touching live wires directly. The probes are insulated and designed for this task. However, follow these basic rules: never insert the probes into an outlet while the multimeter is set to anything other than AC voltage. Never touch the metal tips of the probes while they're in an outlet. Never use a multimeter with cracked or damaged probes.
If you're uncomfortable using a multimeter or if you've checked multiple outlets and they're all reading low, call a licensed electrician. An electrician can check your home's main panel and wiring, which is beyond what a multimeter can diagnose. The cost of a service call is worth it if there's a widespread electrical problem.
Frequently Asked Questions
Can I check outlet voltage without a multimeter?
Not reliably. A multimeter is the only tool that gives you an actual number. Some outlets have a small light that indicates power, but that only tells you whether power is present — not whether the voltage is correct. A multimeter is inexpensive and worth buying if you plan to troubleshoot outlets more than once.
What if my multimeter shows a negative number?
A negative reading usually means you've reversed the probes — the red probe is in the neutral slot and the black probe is in the hot slot. Flip them and take another reading. The absolute value (the number without the minus sign) is what matters for determining whether the outlet is working.
Is 115 volts on a 120-volt outlet a problem?
No. Household voltage naturally fluctuates between about 110 and 125 volts depending on the time of day and how much power your home is using. Anything in that range is normal and safe for standard devices.
Why would an outlet suddenly stop delivering voltage?
The most common reason is a tripped circuit breaker, usually caused by too many devices drawing power at once or a short circuit. Check your breaker panel. If a breaker is in the middle or off position, flip it off completely, then back on. If it trips again when ready, there's a short circuit and you should call an electrician.
Can I check voltage on an outlet while something is plugged in?
Yes. Checking voltage while a device is plugged in actually gives you a more realistic reading because it shows how the outlet performs under load. Just make sure the probes don't touch any part of the plugged-in device.