To read a multimeter, first identify what you need to measure—DC voltage, AC voltage, resistance, continuity, or current. Select the correct function and range, connect the probes to the correct terminals, and read the value shown on the display. For beginners, voltage and continuity measurements are the safest places to start.

What Is a Multimeter?

A multimeter is an electrical testing instrument used to measure quantities such as:

• DC voltage
• AC voltage
• Resistance
• Current
• Continuity
• Diode voltage drop
• Capacitance and frequency on some models

A typical digital multimeter has three main parts:

1. Display — Shows the measured value and units.
2. Function dial/buttons — Select what you want to measure.
3. Input terminals — Determine where the test leads should be connected.

The exact controls vary between models, so always check the meter's manual before using unfamiliar functions. (fluke.com)

Multimeter Symbols You Should Know

The symbols printed around the dial tell you what the meter can measure.

The exact symbol can differ slightly between multimeter models.

Do not select a function based only on the position of the dial. Read the symbol next to the setting.

How to Read a Multimeter Correctly

The basic process is:

1. Identify the electrical quantity you need to measure.
2. Select the correct function.
3. Put the black lead into COM.
4. Put the red lead into the correct input terminal.
5. Select an appropriate range if the meter is manual-ranging.
6. Connect the probes correctly.
7. Read the number and unit on the display.

For voltage, the probes are connected across the circuit or component. For current, the meter must be placed in series with the circuit. This difference is critical because connecting a current input directly across a voltage source can create a near-short circuit. (fluke.com)

Understanding the Multimeter Display

Suppose the screen shows:

12.36 V

This means the meter is measuring:

• Value: 12.36
• Unit: volts
• Measurement: determined by the selected voltage mode

If the display shows:

0.00 V

it may mean the voltage is zero, the probes are connected incorrectly, or you are measuring at the wrong points.

If it shows:

OL

the meaning depends on the selected function. In resistance mode, for example, it commonly indicates an open circuit or a value beyond the selected range.

Always interpret the number together with the selected function and unit.

How to Measure DC Voltage With a Multimeter

DC voltage is used for batteries, Arduino boards, sensors, power supplies and most low-voltage electronics.

Example: Measuring a 9V battery

Step 1: Connect the probes

• Black probe → COM
• Red probe → V/Ω

Do not put the red lead into the current/A terminal when measuring voltage.

Step 2: Select DC voltage

Set the dial to:

V⎓ / V—

If the meter is manual-ranging, select a range higher than the expected voltage.

For a 9V battery, a 20V DC range would be appropriate on a meter that provides that range.

Step 3: Touch the probes to the battery

• Red probe → positive terminal
• Black probe → negative terminal

Step 4: Read the display

A healthy nominal 9V battery might show a reading around its rated voltage, depending on its state of charge and load conditions.

If the probes are reversed, many digital multimeters show the same magnitude with a minus sign.

For example:

-8.7V

means the polarity of the probes is opposite to the meter's positive reference.

Fluke's general procedure for DC voltage measurement is to select the DC voltage function and connect the common lead first, with the voltage lead connected to the appropriate input. (fluke.com)

How to Measure Voltage From an Arduino Power Supply

Suppose you want to check whether a power supply is providing approximately 5V.

Connection

Power supply +  → Red probe
Power supply -  → Black probe

Set the meter to DC voltage.

If the display reads:

4.98V

the supply is providing approximately 5V.

If it reads:

0V

check:

• Probe connection
• Power supply output
• Ground connection
• Meter mode
• Meter range

Important

Voltage is measured across two points.

Do not place the meter in series with the power supply when measuring voltage.

How to Measure AC Voltage With a Multimeter

AC voltage is commonly found in mains-powered equipment and AC electrical systems.

The meter should be set to:

V~

The probes are placed across the two points whose voltage you want to measure.

For example, when measuring an AC source, the meter displays the measured voltage in volts.

Important safety warning

Mains voltage can cause serious injury or death.

A beginner should not use a multimeter on household mains simply as a learning exercise. If you need to work on mains circuits, use a properly rated meter and leads and follow applicable electrical safety procedures. Fluke recommends using an instrument rated for the measurement environment and working on de-energized circuits whenever possible. (fluke.com)

How to Measure Resistance With a Multimeter

Resistance is measured in ohms (Ω).

Resistance measurements should normally be made on a de-energized circuit.

Example: Measuring a resistor

Suppose you have a resistor marked 1kΩ.

1. Turn off the circuit.
2. Disconnect the resistor or isolate it from the circuit when necessary.
3. Black lead → COM.
4. Red lead → V/Ω.
5. Select Ω.
6. Touch one probe to each end of the resistor.
7. Read the display.

A reading such as:

0.99 kΩ

is approximately 990Ω.

Why should power be off?

The meter applies a small test signal to determine resistance. An external voltage can interfere with the measurement and potentially damage the meter.

Fluke recommends turning circuit power off and discharging high-voltage capacitors before resistance, continuity, diode or capacitance measurements. (fluke.com)

How to Test Continuity With a Multimeter

Continuity testing checks whether there is a low-resistance electrical path between two points.

The continuity symbol is commonly represented by a sound-wave or buzzer symbol.

How to test continuity

1. Turn the circuit OFF.
2. Put the black lead in COM.
3. Put the red lead in V/Ω.
4. Select continuity mode.
5. Touch the probes together first.
6. The meter should beep on many models.
7. Touch the probes to the two points you want to test.

A beep indicates that the meter detects continuity according to its internal threshold. The exact resistance threshold for the beep varies by meter. (fluke.com)

What can you test?

Continuity mode is useful for checking:

• Wires
• Switches
• Connectors
• Fuses
• PCB traces
• Cables

For example, a good fuse normally shows continuity, while a blown fuse shows an open circuit. (fluke.com)

How to Measure Current With a Multimeter

Current measurement is different from voltage measurement.

Voltage is measured in parallel. Current is measured in series.

This means the current must flow through the multimeter.

Basic setup

Power supply + → Multimeter → Load → Power supply -

The current flows through the meter and then through the load.

Typical procedure

1. Estimate the maximum current before connecting the meter.
2. Put the black lead into COM.
3. Put the red lead into the appropriate mA/µA or A terminal.
4. Select the correct current function.
5. Break the circuit.
6. Insert the multimeter in series.
7. Read the current.

Example

If an Arduino circuit draws:

0.18A

the multimeter may display:

180mA

provided you are using the appropriate current range.

Why You Can Blow the Multimeter Fuse

This is one of the most common beginner mistakes.

Suppose the red probe is still connected to the A terminal because you were measuring current.

You then switch the dial to voltage and place the probes across a battery.

The meter's current input has very low resistance. Connecting it directly across a voltage source can create a very high current through the meter's internal current path.

This can blow the internal fuse and, with an inadequately protected meter, create a serious safety hazard. (fluke.com)

The habit that prevents this

Before measuring voltage, check that the red lead is in the V/Ω terminal.

Before measuring current:

Move the red lead to the appropriate current terminal.

After measuring current:

Move it back to V/Ω before measuring voltage.

What Do the CAT Ratings on a Multimeter Mean?

CAT ratings indicate the electrical environment in which a measurement instrument is designed to be used.

Common categories include:

• CAT II
• CAT III
• CAT IV

They relate to transient overvoltage environments and the installation location, not simply the maximum continuous voltage.

Basic interpretation

The required category depends on where the measurement is being made. A higher category is generally associated with locations closer to the electrical source and potentially higher-energy transients. (fluke.com)

Why does CAT rating matter?

A meter's CAT rating is part of its safety design. The rating should be appropriate for the electrical environment, and the test leads/accessories must also be suitable.

Do not assume that a meter marked “600V” is safe for every 600V measurement. The CAT category matters too.

How to Choose the Correct Multimeter Range

Multimeters can be:

• Manual ranging
• Auto-ranging

Manual-ranging multimeter

You select the measurement range yourself.

For example, if you expect approximately 12V DC, select a range above 12V.

If the range is too low, the meter may display OL or an overload indication.

Auto-ranging multimeter

The meter automatically selects an appropriate range.

This makes measurement easier for beginners, but you still need to select the correct measurement type.

Auto-ranging does not make an incorrectly selected function safe.

You can still damage a meter by using the current input to measure voltage.

How to Read Negative Voltage on a Multimeter

A negative reading does not necessarily mean something is wrong.

Suppose you measure a battery and get:

-9.2V

This usually means the red probe is connected to the battery's negative side and the black probe to its positive side.

Reverse the probes:

+9.2V

The magnitude remains approximately the same, but the polarity changes.

For DC circuits, the minus sign tells you the measured polarity is opposite to the meter's expected probe orientation.

How to Measure a Battery With a Multimeter

A multimeter is useful for checking the voltage of batteries.

Example: AA battery

1. Set the meter to DC voltage.
2. Black lead → COM.
3. Red lead → V/Ω.
4. Red probe → battery positive.
5. Black probe → battery negative.
6. Read the voltage.

For a nominal 1.5V cell, the actual reading depends on battery chemistry, state of charge and whether the battery is under load.

What the reading tells you

A voltage measurement can tell you the battery's present terminal voltage.

It does not by itself tell you the battery's remaining capacity accurately.

A battery can show a reasonable open-circuit voltage and still perform poorly under load.

How to Measure Voltage With a Multimeter: Practical Example

Suppose an Arduino project is powered by a 12V DC adapter and you want to verify its output.

Expected value

12V DC

Setup

• Black → COM
• Red → V/Ω
• Dial → DC voltage
• Connect probes across the adapter output

Suppose the display shows:

12.08V

The supply is producing approximately 12.08V under the measurement conditions.

If the display shows:

-12.08V

reverse the probes.

If it shows:

0V

check whether:

• The supply is switched on.
• You are measuring the correct terminals.
• The probes have good contact.
• The meter is set to DC voltage.

Common Multimeter Mistakes Beginners Make

1. Using the wrong input terminal

The red lead may be connected to the A or mA jack when it should be in V/Ω.

Fix: Check the terminal before every measurement.

2. Measuring resistance on a powered circuit

This can produce incorrect readings or damage the meter.

Fix: Turn off power before resistance measurements.

3. Measuring current in parallel

Connecting the meter in current mode directly across a voltage source can create a short circuit through the meter's current path.

Fix: Current measurements must be made in series. (fluke.com)

4. Selecting AC instead of DC

A DC battery should be measured using the DC voltage setting, not V~.

5. Ignoring the range

On manual-ranging meters, selecting a range below the expected value can produce an overload indication.

6. Testing continuity on a live circuit

Continuity and resistance testing should generally be performed with the circuit de-energized.

7. Ignoring CAT ratings

A meter suitable for low-voltage electronics may not be suitable for mains distribution measurements.

8. Using damaged probes

Cracked insulation, exposed conductors or loose connectors can create a serious safety risk. Inspect the meter and test leads before use. (fluke.com)

Multimeter Safety Checklist

Before taking a measurement:

• Inspect the meter for damage.
• Inspect the test leads and probe insulation.
• Identify the voltage or current you expect.
• Select the correct measurement function.
• Put the black lead in COM.
• Confirm the red lead is in the correct terminal.
• Check the meter's CAT rating for the measurement environment.
• Start with an appropriate range.
• Keep your fingers behind the probe guards.
• Avoid unnecessary contact with exposed conductors.
• Disconnect power before resistance and continuity testing.
• Never bypass or replace a meter fuse with wire.
• Use properly rated leads and accessories.

For live electrical measurements, the meter and accessories should be rated for the environment. Fluke also recommends verifying that the test instrument is functioning correctly before use. (fluke.com)

Multimeter Measurement Cheat Sheet

The exact terminals and functions vary by multimeter, so use the meter's manual when in doubt.

How to Read a Multimeter: Quick Reference

If you remember only five rules, remember these:

1. Voltage → measure across the circuit.

2. Current → put the meter in series.

3. Resistance/continuity → power OFF.

4. Voltage measurement → red lead in V/Ω.

5. Check CAT rating before measuring higher-energy circuits.

These basic rules prevent many common measurement errors.

Final Verdict

Learning how to read a multimeter starts with identifying the measurement type and using the correct terminals, function and connection method. For beginners, start with low-voltage DC measurements such as batteries and Arduino power supplies, then learn resistance and continuity with the circuit powered off.

Current measurement requires more care because the meter becomes part of the circuit. For mains and other high-energy systems, use a properly rated meter and leads and follow appropriate electrical safety procedures.