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

A multimeter is a handheld tool that measures electrical properties. To check voltage, you need to turn the dial to a voltage setting — usually marked with a V symbol, sometimes with a wavy line (AC voltage) or a straight line (DC voltage). Most household electronics and batteries use DC voltage, so start there unless you're testing wall outlets or appliances that run on AC power.

The dial also shows different ranges: 2V, 20V, 200V, 2000V. Pick the range closest to but higher than the voltage you expect to measure. If you're testing a 9-volt battery, set it to 20V. If you're testing a car battery (12 volts), also use 20V. If you're unsure what voltage to expect, start at the highest range and work down — this protects the meter from damage.

Key Takeaways

  • Turn the dial to the voltage setting (V symbol) and choose a range higher than the voltage you expect to measure.
  • Insert the black probe into the COM (common) port and the red probe into the V port on the meter's face.
  • Touch the black probe to the negative terminal or ground and the red probe to the positive terminal or wire you're testing.
  • Read the number on the display — it shows the voltage between the two points you're touching.
  • For AC voltage (wall outlets), switch to the AC setting (wavy V symbol) and follow the same steps.

Connect the probes to the correct ports on the meter

Every multimeter has ports along the bottom where you plug in the two probes. The black probe always goes into the port labeled COM (common or ground). The red probe goes into the port labeled V (voltage) — sometimes labeled mA or A if you're measuring current instead, but for voltage it's always V.

Push the probe tips firmly into the ports until they click or seat fully. A loose connection will give you a reading that jumps around or shows zero even when voltage is present. If the probes feel loose after inserting them, the meter's ports may be worn and need replacement — this is a common reason an old meter stops working reliably.

Touch the probes to the two points you want to measure between

Voltage is always measured between two points. The black probe touches the negative side (the ground, the minus terminal, or the return path), and the red probe touches the positive side (the power source or the wire you're testing). For a battery, touch black to the flat end (negative) and red to the bump (positive). For a wall outlet, touch black to the longer slot and red to the shorter slot.

Hold the probes steady against the points you're measuring. The display will show a number almost instantly. If the number is negative, you reversed the probes — swap them and the reading will flip to positive. A negative reading doesn't damage the meter; it just means you measured in the opposite direction.

Read the voltage number on the display

The display shows the voltage as a number, usually with one or two decimal places. If you set the range to 20V and the display reads 9.2, that means 9.2 volts. If the display shows 1, you're reading 1 volt. The range you selected determines how the number is interpreted — at 200V range, a display reading of 12 means 12 volts; at 2V range, the same reading would mean 0.012 volts (which would be wrong for that situation, so you'd switch ranges).

If the display shows "OL" or "1" with nothing else, the voltage is too high for the range you selected — turn the dial to a higher range and try again. If the display shows 0.00 and you expected voltage, check that the probes are making good contact and that you're touching the right points. Corrosion, loose connections, or a dead battery can all cause zero readings when voltage should be present.

Test AC voltage from wall outlets and appliances

AC voltage (alternating current) comes from wall outlets and powers most household appliances. To measure it, turn the dial to the AC voltage setting — it's marked with a wavy V symbol, usually separate from the DC V symbol. Set the range to 200V or 250V for wall outlets in North America (which supply around 120V) or Europe (which supplies around 230V).

Touch the black probe to the longer slot of the outlet and the red probe to the shorter slot. The display will show a number around 110–120V in the US or 220–240V in Europe. With AC voltage, polarity doesn't matter the way it does with DC — the probes can be reversed and you'll get the same reading. However, for safety, always treat the shorter slot as live (hot) and the longer slot as neutral, and keep your fingers away from the metal probe tips.

Troubleshoot when the reading doesn't match what you expect

If a battery reads 0V when it should read 9V or 12V, the battery is likely dead. If a wall outlet reads 0V, check that the outlet is switched on and that something is actually plugged in — some outlets only power when a device is drawing current. If a car battery reads 10V instead of 12V, the battery is weak and may need charging or replacement.

If the reading bounces around or changes rapidly, the connection is loose. Press the probe tips harder against the contact points, or clean the contact points with a dry cloth to remove corrosion. If you're testing a wire inside an appliance, make sure the probe tip is piercing the insulation and touching the bare wire — a probe resting on plastic insulation will read zero even if current is flowing inside.

Understand what the voltage reading tells you

Voltage is the electrical pressure pushing current through a circuit. A higher voltage doesn't necessarily mean more power — that depends on current too — but it tells you whether a power source is working. A battery that reads 0V is dead. A battery that reads half its rated voltage is weak. A wall outlet that reads 0V is either off, broken, or the breaker has tripped.

Voltage also tells you whether a device is receiving power at a particular point. If you measure 12V at a car battery but 0V at a light bulb connected to it, the wire between them is broken or disconnected. If you measure 12V at both points, the wire is intact and power is reaching the bulb — the problem is likely the bulb itself or the ground connection.

Frequently Asked Questions

Can I check voltage on a live wire without turning off the power?

Yes — checking voltage is a non-contact measurement, so you're not drawing current. However, stay safe: wear insulated gloves, keep your fingers away from the probe tips, and never touch both probes to the same wire at the same time. If you're uncomfortable working near live wires, turn off the power first.

What's the difference between DC and AC voltage?

DC (direct current) flows in one direction and comes from batteries, solar panels, and car electrical systems. AC (alternating current) switches direction many times per second and comes from wall outlets and power lines. Most multimeters measure both, but you have to select the right setting or the reading will be wrong.

Why does my multimeter show a different voltage than the label says?

Batteries lose voltage as they age and discharge, so a 9V battery might read 8.5V or lower. Wall outlets can vary by a few volts depending on demand on the grid. If the reading is much lower than expected, the battery or power supply is weak or failing.

Do I need to turn off the device before checking voltage?

No — voltage measurement doesn't require the device to be off. In fact, you often want to measure voltage while a device is running to see whether it's receiving power. Only turn off power if you're working on wiring or connections and need to be safe from electric shock.

What happens if I set the range too low?

The display will show "OL" (overload) or "1" and won't give you a reading. Turn the dial to a higher range and try again. Setting the range too low won't damage the meter, but setting it too high will give you a reading with less precision — a 200V range is less precise than a 20V range for measuring a 9V battery.