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How to Measure Current in a Series Circuit Using Multimeter

The person typing “how to measure current in a series circuit using multimeter” wants to know how to read the current that flows through a loop of components connected one after another. Unlike voltage, current is measured by putting the meter into the path, so the loop has to be opened and the meter placed in series. The reading is the same at any point in a series string, because the same current flows through every component.

Quick answer

• Turn off the circuit power before you open the loop.
• Plug the black lead into COM and the red lead into the current jack (A or mA, depending on the expected current).
• Open the loop at one point and connect the meter across the break, so all the current flows through the meter.
• Restore power, read the display, then turn the power off before you remove the meter.

Why the reading is the same everywhere in a series string

The Keysight engineering guide on series and parallel circuits states that “the same current flows through each component in the circuit without any branching off.” That single sentence is the reason this measurement is easy in a series circuit. You can open the loop at any point, insert the meter, and the reading will match what every other point in the string would show. You do not need to measure each part separately.

Keep in mind that the reading tells you the current through the string, not the voltage across any part. If you need the voltage drop on a part, use the voltage method instead. For the basics of how voltage, current and resistance relate, Fluke’s guide to Ohm’s law gives the formula, stating that the relationship is voltage equals current times resistance. Rearranged, current equals voltage divided by resistance.

Equipment and jacks

Use a multimeter with a current function and at least one current jack. Fluke’s multimeter guide explains that most meters have three terminals: the common (COM) terminal, the voltage (V) terminal, and the current (A) terminal. For current, COM is the black lead and the current jack is the red lead. Some meters have a separate jack for small currents (mA) and one for larger currents (A). Pick the jack that matches the expected current. If you do not know the current, start with the higher-current jack.

Check the meter’s fuse before you measure current. Fluke’s guide says to “always check the multimeter’s fuse before making a current measurement.” A blown fuse gives no reading, and a meter used on the wrong jack can damage the fuse or the meter.

Step-by-step: measure series current

1. Turn off the circuit power. Current measurements require opening the loop, so power must be off before you touch any conductor.
2. Set the dial to current. Choose DC or AC current to match the circuit, and choose a range that covers the expected current.
3. Insert the leads. Put the black lead in COM and the red lead in the current jack.
4. Open the loop. Disconnect one wire or remove one component end so that the current path is broken at one point.
5. Connect the meter in series. Place the meter probes across the break so the current has to pass through the meter. This is the step that makes it a series measurement.
6. Restore power and read. Turn the power on and read the display. Note the unit (A or mA).
7. Turn the power off again. Before you remove the meter, cut the power.
8. Remove the meter and close the loop. Reconnect the wire or component end, then check the circuit before restoring full power.

The steps above follow the general method in Fluke’s multimeter guide and the series rule in the Keysight guide. Fluke’s guide to measuring current with a clamp meter describes a way to read current without opening the circuit, but that method uses a different tool. This guide covers the multimeter method only.

Reading the number and checking it

Once the reading is on the display, compare it with what you expect. You can estimate the current from Ohm’s law if you know the source voltage and the total resistance. For a series string, the total resistance is the sum of the resistances, as the Keysight guide states: R_total = R1 + R2 + … + Rn. Dividing the source voltage by that total gives the expected current. A reading far from that estimate points to a wrong jack, a bad connection, a fault in the circuit, or a component that is not what its label says.

If the display shows OL or no reading at all, the meter may be on the wrong jack, the fuse may be blown, or the loop may still be open somewhere else. Check each in that order. Do not increase the range or force the reading by changing the jack while the power is on.

Common mistakes

• Leaving the leads in the current jacks and connecting across a live source. The meter then acts as a short. Fluke warns against placing the leads across a circuit in parallel while they are in the current jacks.
• Measuring current with the power on. Open the loop with power off, then power up.
• Using the mA jack for a high current. Use the jack rated for the expected current.
• Forgetting to restore the circuit. Close the loop before you turn the circuit on for normal operation.

How we chose

This guide uses the current-measurement steps from manufacturer and engineering sources we opened and read in full. We picked the steps that apply to a general multimeter and kept the wording close to what those sources say. We did not use retail pages or product listings for any technical statement.

What we could not verify

• The Klein Tools MM300 manual is a PDF that the fetch tool could not read as text. Its exact current-jack labels and current limits are not quoted here. Read your own meter’s manual for those values.
• The Fluke pages we opened do not contain a full step-by-step series-current procedure. The open-the-loop steps above are the general method, and the sources we opened confirm the jack, fuse, and power-off points.
• No fuse rating or current limit for any specific meter is given, because the sources we opened do not state one.

FAQ

Do I have to break the circuit to measure series current?

Yes, for a multimeter. The meter has to sit in the current path. A clamp meter can read current without opening the circuit, but that is a different tool.

Why is the current the same everywhere in a series circuit?

The Keysight guide states that the same current flows through each component without branching. That is why one measurement represents the whole string.

Which jack do I use for the red lead?

Use the current jack that matches the expected current. Fluke’s guide names the current terminal as the A terminal, and many meters split it into A and mA.

What if the meter shows OL?

Check the jack, the fuse, and whether the loop is closed elsewhere. OL usually means the current is over the range or the meter is not in the path.

Can I measure current with the leads in the voltage jack?

No. A current measurement needs the current jack. Voltage in the current path can short the circuit and damage the meter.

Should I power the circuit before removing the meter?

No. Turn the power off before you remove the meter, then close the loop.

Bottom line

To measure current in a series circuit, power off, open the loop, put the meter in series with the red lead in the current jack, power on, read, then power off again. The same current reads the same at every point in the string.

Related guides

For meters that work for this kind of job, read our guide to Extech multimeters and our guide to Fluke clamp meters for automotive work.

Sources

• Fluke, “How to Use a Multimeter: A Comprehensive Guide”: https://www.fluke.com/en-us/learn/blog/maintenance-monitoring/how-to-use-a-multimeter-guide (opened 2026-10-28)
• Fluke, “What Is Ohm’s Law?”: https://www.fluke.com/en-us/learn/blog/electrical/what-is-ohms-law (opened 2026-10-28)
• Keysight, “Series and Parallel Circuits: Engineering 101 Guide”: https://www.keysight.com/used/kr/en/knowledge/guides/series-and-parallel-circuits (opened 2026-10-28)
• Fluke, “How to Measure DC Voltage with a Digital Multimeter”: https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-measure-dc-voltage-with-a-digital-multimeter (opened 2026-10-28)