Set your multimeter to voltage mode before touching any wires

To check voltage with a multimeter, turn the dial to the voltage setting that matches what you're measuring. Most multimeters have two voltage options: DC (direct current, marked with a straight line) and AC (alternating current, marked with a wavy line). Household outlets use AC; batteries and phone chargers use DC. If you're not sure which one you need, start with AC — it's the more common measurement in home settings.

Once you've selected the right mode, choose a range that's higher than the voltage you expect to find. If you're checking a 9-volt battery, set the dial to 20V or higher. If you're checking a wall outlet, set it to 250V or higher. Starting too low can damage the meter or give you a false reading.

Key Takeaways

  • Turn the dial to DC or AC voltage mode depending on what you're testing — DC for batteries and chargers, AC for wall outlets.
  • Always set the range higher than the voltage you expect to measure to avoid damaging the meter.
  • Touch the black probe to ground or the negative side and the red probe to the positive side or the point you want to measure.
  • The number on the display is the voltage; if it shows a negative number, you've reversed the probes, which is harmless.
  • Never use a multimeter on live circuits if you're not trained — stick to batteries, chargers, and outlets you can safely access.

Connect the probes to the right points

Every multimeter comes with two probes: a black one and a red one. The black probe always goes to ground or the negative side of what you're testing. The red probe goes to the positive side or to the point where you want to measure voltage. For a battery, touch black to the flat end and red to the bump. For a wall outlet, touch black to the longer slot and red to the shorter slot.

If you're testing a circuit board or a wire inside a device, you may need to touch the probes to specific points. The manual for your device will show you where. If you reverse the probes by accident, the meter will show a negative number instead of a positive one — this won't hurt anything, and you can just flip them and try again.

Read the number on the display

Once the probes are in place, look at the screen. The number you see is the voltage. If you're checking a 9-volt battery and the display shows 8.7V, that battery is still good. If it shows 7V or lower, the battery is running low. For a wall outlet in North America, you should see around 120V. In Europe and many other places, you should see around 230V.

If the display shows 0V or nothing at all, either the device has no power, the probes aren't making good contact, or you've set the meter to the wrong mode. Try wiggling the probes slightly to make sure they're touching the surface. If that doesn't work, double-check that you've selected voltage mode and not resistance or continuity mode.

Understand the difference between DC and AC

DC voltage flows in one direction, like water through a pipe. Batteries, phone chargers, car batteries, and most electronics inside devices use DC. When you measure DC, the polarity matters — the red probe must touch the positive side, or you'll get a negative reading.

AC voltage switches direction back and forth, many times per second. Wall outlets, power lines, and the electricity that comes into your house is AC. When you measure AC, polarity doesn't matter — you'll get the same reading either way. AC is also more dangerous to touch directly, so be extra careful around live outlets.

Know when to use autorange instead of manual range

Many modern multimeters have an autorange button or setting. When autorange is on, the meter picks the right range for you automatically. This is convenient and safer for beginners because you don't have to guess whether to use 20V or 200V. The downside is that autorange is slightly slower — it takes an extra second or two to settle on a reading.

If your meter has autorange, use it unless you're taking many measurements in a row and speed matters. If you're setting the range manually, start high and work your way down. A reading of 12.5V on the 200V range is accurate. A reading of 12.5V on the 20V range is also accurate. But if you set it to 2V and the voltage is actually 12V, the meter may show an error or give you a wrong number.

Stay safe around live circuits and outlets

Measuring voltage on a battery or a powered-off device is safe. Measuring voltage on a live wall outlet or a powered circuit is riskier. If you're not trained in electrical work, avoid touching live circuits. If you must measure a live outlet, touch only the probe tips to the slots — never touch the metal parts of the probes themselves.

Wear shoes with rubber soles, keep one hand in your pocket or behind your back so current can't flow through your chest, and never measure voltage while standing in water or on a wet floor. If you're uncomfortable working with live electricity, ask a licensed electrician to do it for you. No measurement is worth an injury.

Troubleshoot common problems

If your meter shows a very high number or "OL" (overload), you've set the range too low. Turn the dial to a higher range and try again. If the meter shows 0V when you expect to see voltage, check that the probes are making solid contact with the surface. Corrosion, dirt, or a loose connection can block the signal.

If the meter won't turn on, the battery inside may be dead. Most multimeters use a 9V battery or two AA batteries. Open the battery compartment on the back, check that the battery is installed correctly, and replace it if it's old. If the meter still won't work after a new battery, the meter itself may be broken and will need to be replaced.

Frequently Asked Questions

What's the difference between a digital and analog multimeter?

A digital multimeter shows the voltage as a number on a screen, making it easy to read. An analog multimeter uses a needle that moves across a scale, which takes more practice to read accurately. Digital meters are more common now and are easier for beginners.

Can I measure voltage on a live wire without removing insulation?

No. The insulation blocks the probe from reaching the wire. You have to strip a small section of insulation or touch the probe to a bare part of the wire. If you're not comfortable doing this, don't — ask an electrician instead.

What does it mean if the voltage keeps changing on the display?

A changing reading usually means the connection is loose or the device is drawing power unevenly. Try pressing the probes more firmly against the surface. If the reading still bounces around, the device may be faulty or the meter may need calibration.

Is it safe to measure voltage on a phone charger?

Yes. Unplug the charger first, then measure the voltage on the output side (where the cable connects). You should see the voltage printed on the charger itself — usually 5V for phones. If the meter shows something very different, the charger may be broken.

Why does my meter show a negative number?

You've touched the red probe to the negative side and the black probe to the positive side — the opposite of what you should do. Flip the probes and try again. A negative reading won't damage anything; it just means the polarity is reversed.