How to Measure Amps with a Multimeter: 10A, 20A & Current Measurement Guide

Measuring current is one of the most useful functions of a digital multimeter, but it is also one of the easiest measurements to perform incorrectly. Unlike voltage measurement, where probes are placed across two points, current measurement with a conventional multimeter normally requires the meter to become part of the circuit.

What Does “Amps” Mean on a Multimeter?

Amps, or amperes, measure electrical current — the rate at which electric charge flows through a circuit.

A digital multimeter may include several current ranges or functions, commonly shown as:

• A⎓ – DC current
• A~ – AC current
• mA – milliamps
• µA – microamps

Not every multimeter supports every type or range of current measurement. Some compact meters concentrate on voltage, resistance and continuity, while professional instruments may provide dedicated µA, mA and higher-current inputs.

Before measuring current, check the symbols around the input sockets and the manufacturer's specifications for your particular meter.

The Golden Rule: Current Is Normally Measured in Series

Voltage and current are measured differently.

When measuring voltage, a multimeter is normally connected in parallel across two points in a circuit.

When measuring current through the probe inputs of a conventional digital multimeter, the circuit is normally opened and the meter is inserted in series. This allows the circuit current to flow through the multimeter's internal current-measurement path.

Fluke's multimeter documentation similarly describes current measurement by breaking the circuit and connecting the meter across that break. For further technical reference, see Fluke's digital multimeter current-measurement instructions.

Never Place a Multimeter Set to Amps Directly Across a Voltage Source

If a multimeter is configured for current measurement and its probes are placed directly across a battery, power supply or another voltage source, the meter can create a very low-resistance path.

This can:

• Blow the multimeter's current fuse.
• Damage the test leads.
• Damage the meter.
• Damage the circuit being tested.
• Cause sparking or arcing.
• Create a serious electrical hazard.

How to Measure Amps with a Digital Multimeter

The exact controls and input arrangement vary between meters, so always check the manual for your instrument. The following is the normal current-measurement workflow.

1. Identify Whether You Are Measuring AC or DC Current

Select the function appropriate for the circuit:

• A⎓ typically represents DC current.
• A~ typically represents AC current.

Common DC-current applications include:

• Batteries
• Automotive circuits
• Electronic circuits
• PCB diagnostics
• DC power supplies

Do not assume that every multimeter supports AC and DC current on all current ranges. Verify the specification before testing.

2. Connect the Black Probe to COM

The black test lead normally connects to the input marked COM.

3. Connect the Red Probe to the Correct Current Input

A digital multimeter can have several input terminals. Typical markings include:

• VΩ
• µA/mA
• mA
• A
• 10A
• 20A

For higher-current measurements, the red probe normally has to be moved from the voltage/resistance terminal to the dedicated current terminal.

4. Select the Correct Current Function

Set the rotary selector or measurement function to the required mode, such as A⎓, A~, mA or µA.

An auto-ranging multimeter can select the numerical range automatically, but you still need to choose the correct measurement function and use the correct terminal.

If you work with electronics and require additional resolution or advanced measurement capability, see the ZOYI Pro Multimeters range.

5. Isolate the Circuit Where Appropriate

Before opening a circuit and inserting the meter, switch off or isolate the circuit where the test procedure allows.

The UK Health and Safety Executive advises that electrical work should generally be carried out with systems dead wherever possible. Live testing should only be performed when necessary and with suitable equipment, procedures and competence.

See: HSE GS38 – Electrical test equipment for use on low-voltage electrical systems.

6. Connect the Multimeter in Series

Open the circuit at the point where the current is to be measured.

Connect one meter probe to one side of the opened circuit and the second probe to the other side. The circuit current can then pass through the multimeter's current-measurement path.

7. Energise the Circuit and Read the Display

Restore power where appropriate and observe the current reading.

During DC measurements, a negative current reading commonly indicates that the test-lead polarity is reversed relative to the direction of current flow.

8. Disconnect the Meter Safely

10A vs 20A Multimeter: What Is the Difference?

Many digital multimeters include a higher-current input marked 10A or 20A.

These markings describe a current-measurement range under specified operating conditions. They should not automatically be interpreted as a continuous-current rating.

Depending on the meter, the manufacturer may specify:

• A lower range for continuous current measurement.
• A 10A or 20A range intended only for shorter measurements.
• A maximum measurement time.
• A required cooling period between tests.
• A particular fuse specification.

Always follow the specifications for the individual instrument. Two meters carrying a “20A” marking may have very different permitted test durations, fuse arrangements and safety ratings.

Can a Multimeter Measure 20 Amps?

Yes — some multimeters can measure up to 20 amps, but only when specifically designed and rated to do so.

Before attempting a 20A measurement, check:

• The meter's maximum current range.
• The maximum permitted measurement duration.
• The current-input fuse specification.
• The test-lead current rating.
• The circuit voltage.
• The CAT measurement rating.
• The manufacturer's operating instructions.

If the meter is rated for a maximum of 10A, do not attempt to pass 20A through its current input.

When Should You Use a Clamp Meter Instead?

A clamp meter measures current by detecting the magnetic field produced around a conductor.

Unlike conventional in-series current measurement through a multimeter's probe terminals, clamp measurement normally allows current to be measured without opening the circuit.

This makes clamp meters particularly useful when measuring higher currents or when interrupting the circuit would be inconvenient.

Typical applications include:

• Motors
• Pumps
• HVAC equipment
• Appliances
• Distribution circuits
• Workshop equipment
• Electrical maintenance

Fluke describes the distinction simply: a digital multimeter provides detailed general electrical measurements and lower-current capability, while a clamp meter is particularly useful for current measurement without breaking the circuit. See Fluke's clamp meter vs digital multimeter guide.

For higher-current testing, browse the ZOYI UK Clamp Meter range.

Clamp Around One Conductor Only

For normal current measurement with a clamp meter, place the jaws around one conductor.

If live and neutral conductors are enclosed together, their opposing magnetic fields can cancel each other and the meter may show approximately zero or an incorrect value.

For additional clamp-current measurement guidance, see Fluke's current measurement with a clamp guide.

Multimeter vs Clamp Meter for Measuring Current

Why Does a Multimeter Fuse Blow When Measuring Amps?

The current inputs of many digital multimeters contain protective fuses.

Common reasons for blowing a current-input fuse include:

• Exceeding the permitted current.
• Connecting a meter set to amps directly across a voltage source.
• Using the wrong input terminal.
• Selecting the wrong measurement function.
• An unexpected fault or high current in the circuit.

If voltage, resistance and continuity measurements continue to work but the current range no longer registers, a blown current-input fuse is one possible cause.

What Happens If the Red Probe Is in the Wrong Socket?

For voltage, resistance and continuity measurements, the red lead normally connects to the VΩ terminal.

For current measurement, the red lead may need to move to an mA, A, 10A or 20A terminal.

If you finish measuring current but leave the red lead connected to the high-current socket, attempting a subsequent voltage measurement could place the current-measurement path directly across the circuit.

A simple habit can prevent this: return the red lead to the normal VΩ socket immediately after finishing a current measurement.

10A or 20A Multimeter: Which Should You Choose?

A higher current range can be useful, but maximum amperage is only one part of choosing a digital multimeter.

Also consider:

• AC and DC measurement capability
• Expected maximum current
• Current measurement duration
• Fuse protection
• CAT rating
• True RMS capability
• Voltage range
• Display counts
• Measurement accuracy
• Resistance and continuity performance
• Capacitance and frequency measurement
• Auto-ranging
• Test-lead quality

For general electrical and electronics work, browse the ZOYI Digital Multimeters range.

For advanced electronics diagnostics where waveform viewing is also useful, see the ZOYI Oscilloscope Multimeters range.

Common Current Measurement Mistakes

• Measuring current as if it were voltage.
• Connecting a current input directly across a power source.
• Leaving the red test lead in the amp socket after testing.
• Using the mA input for a current that exceeds its rating.
• Assuming a 20A marking means continuous 20A operation.
• Ignoring the meter's fuse specification.
• Using damaged or underrated test leads.
• Ignoring CAT and voltage ratings.
• Trying to measure a high-current circuit when a clamp meter would be more appropriate.
• Assuming every clamp meter measures both AC and DC current.

Frequently Asked Questions

How do you measure amps with a multimeter?

Select the appropriate AC or DC current function, connect the test leads to the correct terminals, open the circuit and connect a conventional probe-type multimeter in series. Never exceed the manufacturer's ratings.

Do you measure current in series or parallel?

Current through a conventional multimeter's current input is normally measured in series. Voltage is normally measured in parallel.

Which multimeter port should I use for amps?

Use the current terminal specified for the expected current range. Depending on the meter, this may be marked µA/mA, mA, A, 10A or 20A.

What does A~ mean on a multimeter?

A~ normally indicates AC current. A⎓ normally indicates DC current.

Can a multimeter measure 20 amps?

Some can, but only if the meter, current terminal, fuse and test leads are designed for that measurement and the manufacturer's maximum measurement time and other operating limits are followed.

Why did my multimeter spark when measuring amps?

Possible causes include placing the meter across a voltage source while configured for current, using the wrong terminal, selecting an incorrect function, or exceeding the instrument's rating. Stop testing and inspect the equipment before using it again.

How do I know if the current fuse is blown?

One possible symptom is that voltage and resistance measurements continue to function but a current range no longer produces a reading. Consult the meter's manual before inspecting or replacing the fuse.

Is a clamp meter better than a multimeter?

Neither is universally better. A digital multimeter is highly versatile and is particularly useful for detailed voltage, resistance, continuity and lower-current measurements. A clamp meter is particularly useful when current needs to be measured without opening the circuit or when the expected current exceeds the practical direct-current-input range of a standard DMM.

Choosing the Right ZOYI Test Meter

ZOYI UK offers digital multimeters, professional high-count meters, oscilloscope multimeters and clamp meters for electronics, electrical diagnostics and workshop applications.

Final Safety Checklist

Choosing the correct measurement method is more important than simply choosing the highest amp range. For general testing, explore the ZOYI UK Digital Multimeter range, or visit ZOYI Clamp Meters for current measurements where opening the circuit is undesirable.