Set the multimeter to the voltage setting that matches what you're testing

A digital multimeter measures voltage, current, and resistance. To check voltage, you first turn the dial to the voltage setting. Most multimeters have separate settings for DC voltage (marked V with a straight line) and AC voltage (marked V with a wavy line). DC voltage powers most household electronics — phones, computers, batteries. AC voltage comes from wall outlets and power lines.

Start by choosing the right range. If you don't know the voltage, begin with the highest DC or AC setting available on your meter. Once you get a reading, you can switch to a lower range for more precision. A reading of 12 volts on a 200-volt range is less accurate than 12 volts on a 20-volt range, but it's safe to start high and work down.

Key Takeaways

  • Turn the dial to DC voltage (V with a line) for batteries and electronics, or AC voltage (V with a wave) for wall outlets and power lines.
  • Touch the black probe to ground or the negative side and the red probe to the positive side or the point you're testing.
  • Read the number on the screen — it shows the voltage between the two probe points.
  • If the screen shows a minus sign, you have the probes reversed, but the number itself is still correct.
  • Start with the highest voltage range if you're unsure, then switch to a lower range for a more precise reading.

Connect the probes to the right points

Every multimeter comes with two probes: a black one and a red one. The black probe connects to the COM (common) port on the meter. The red probe connects to the V port (or sometimes a port marked for both voltage and resistance). These are usually labeled on the meter itself.

When testing, touch the black probe to the negative side or ground point, and touch the red probe to the positive side or the point you want to measure. For a battery, black goes on the flat end (negative terminal) and red goes on the bump (positive terminal). For a wall outlet, black goes in the longer slot and red goes in the shorter slot. For a circuit or wire, black touches ground or the return path, and red touches the live wire or the point being tested.

Read the voltage on the screen

Once both probes are in place, the multimeter displays a number. That number is the voltage between the two points. A 9-volt battery reads around 9 volts. A wall outlet in the United States reads around 120 volts AC. A car battery reads around 12 to 14 volts DC when the engine is running.

If the screen shows a minus sign in front of the number, you have the probes reversed — the red probe is on the negative side and the black probe is on the positive side. The number itself is still correct; the minus sign just tells you the polarity is backwards. You can flip the probes or ignore the minus sign, depending on what you need to know.

Understand DC voltage versus AC voltage

DC voltage flows in one direction and is what batteries and most electronics use internally. AC voltage alternates direction many times per second and is what comes from wall outlets. The two require different meter settings because they behave differently.

If you measure AC voltage with the DC setting, you'll get a reading of zero or a very small number, because the meter is looking for voltage that flows in one direction. If you measure DC voltage with the AC setting, you'll also get zero or a very small number. Always match the setting to the source: use DC for batteries, phone chargers, car systems, and circuit boards; use AC for wall outlets, power cords, and anything plugged into the wall.

Test common household items safely

A wall outlet is the easiest place to practice. Set the meter to AC voltage on the 200-volt range. Insert the black probe into the longer slot and the red probe into the shorter slot. You should see a reading around 110 to 120 volts. Do not touch the metal parts of the probes while they are in the outlet.

For a battery, set the meter to DC voltage on the 20-volt range. Touch the black probe to the negative terminal (the flat end) and the red probe to the positive terminal (the bump). A fresh AA battery reads around 1.5 volts. A 9-volt battery reads around 9 volts. A car battery reads around 12 to 14 volts when the engine is off, and 13 to 15 volts when running.

For a phone charger or laptop power supply, set the meter to DC voltage. Most chargers output between 5 and 20 volts. Check the label on the charger to see what voltage it should produce, then measure the output at the connector to see if it matches. If the charger is plugged in and you're measuring the output connector, you're measuring DC voltage, not AC.

Troubleshoot when the meter shows zero or an unexpected reading

If the meter shows zero when you expect a voltage, check that the probes are touching the right points. A loose connection or a probe touching paint or corrosion instead of bare metal will give a zero reading. Clean the contact points with a dry cloth and try again.

If the meter shows a very small number when you expect a larger one, you may have the wrong setting selected. Double-check that you're on DC or AC voltage, not resistance or current. If you're on the wrong range (for example, the 200-volt range when measuring a 9-volt battery), switch to a lower range for a more accurate reading.

If the meter shows a number that's way too high or too low, the probes may be reversed or touching the wrong part of the circuit. For a battery, make sure black is on the negative terminal and red is on the positive terminal. For a wall outlet, make sure black is in the longer slot and red is in the shorter slot. If the reading is still wrong, the battery or outlet may be dead or faulty.

Know when to stop and ask for help

Measuring voltage at a wall outlet or a battery is safe. Measuring voltage inside a plugged-in appliance or near high-voltage equipment like a breaker panel is not. If you're unsure whether something is safe to measure, do not touch it. Electricity can cause serious injury or death.

If you're testing something you've never measured before, start with the highest voltage range and work down. This protects the meter from damage if the voltage is higher than you expect. If the meter shows a reading that doesn't make sense — like 240 volts from a battery or 0 volts from a wall outlet — stop and check your setup before trying again.

Frequently Asked Questions

What's the difference between the V with a line and the V with a wave?

The V with a straight line is DC voltage, used for batteries and electronics. The V with a wavy line is AC voltage, used for wall outlets and power lines. Using the wrong setting gives you a zero or very small reading because the meter is looking for the wrong type of voltage.

Can I damage my multimeter by measuring the wrong thing?

Yes. If you measure current (amps) on the voltage setting, or measure very high voltage on a low range, you can blow a fuse inside the meter or damage the display. Always start with the highest voltage range if you're unsure, and never measure current unless you know what you're doing.

Why does my meter show a minus sign?

A minus sign means the red probe is touching the negative side and the black probe is touching the positive side — the probes are reversed. The voltage number is still correct. You can flip the probes or leave them as they are, depending on what you need to know.

How do I know if a battery is dead?

A fresh AA battery reads around 1.5 volts, a fresh 9-volt battery reads around 9 volts, and a car battery reads around 12 to 14 volts when the engine is off. If a battery reads significantly lower — like 0.5 volts for an AA or 6 volts for a 9-volt — it is likely dead or nearly dead.

Is it safe to measure voltage at a wall outlet?

Yes, measuring AC voltage at a wall outlet is safe if you follow basic precautions: keep your fingers away from the metal probe tips, do not touch both probes at the same time, and do not measure inside appliances or near breaker panels. If you're unsure, do not measure it.