What a multimeter tells you about a capacitor

A multimeter can tell you whether a capacitor is completely dead, holding a charge, or working normally — but it cannot measure the exact capacitance value the way a dedicated capacitor meter can. Most multimeters have a capacitance setting that gives you a rough reading, and all multimeters can use the resistance mode to spot a capacitor that has failed short or open.

The test takes about two minutes and requires you to discharge the capacitor first (a safety step), set the multimeter to the right mode, and touch the probes to the capacitor's leads. A working capacitor will show a reading that climbs gradually toward infinity on the resistance scale, or display a capacitance value on the capacitance scale if your multimeter has one.

This guide covers the most common test — using the resistance mode to check whether a capacitor is shorted or open — and also explains how to read a capacitance measurement if your multimeter has that setting.

Key Takeaways

  • Always discharge the capacitor by touching a screwdriver across both leads before you test it, because a charged capacitor can shock you or damage your multimeter.
  • The resistance mode test works on any multimeter: a reading that climbs toward infinity means the capacitor is good, while a reading stuck at zero or very low means it has failed.
  • If your multimeter has a capacitance setting (marked with a symbol like µF or nF), you can measure the actual capacitance value and compare it to the number printed on the capacitor's body.
  • Electrolytic capacitors are polarized and must be tested with the red probe on the positive lead and the black probe on the negative lead, or the reading will be unreliable.

Discharge the capacitor before you touch it

A charged capacitor can deliver a painful shock or destroy your multimeter's internal circuitry. Before you do anything else, you must discharge it safely. Take an insulated screwdriver — one with a plastic handle — and touch the metal shaft across both leads of the capacitor at the same time. You will see a small spark; that is the capacitor releasing its stored charge.

If the capacitor is mounted on a circuit board, you can also discharge it by turning off the device, unplugging it, and waiting at least five minutes. Many circuits have built-in resistors that bleed off the charge automatically. However, the screwdriver method is faster and more reliable, so use it if the capacitor is accessible.

After you discharge the capacitor, do not touch the leads with your bare fingers while you are testing. The oils on your skin can affect the reading, especially on high-value capacitors.

Test with the resistance mode (works on any multimeter)

Set your multimeter dial to the resistance mode, usually marked with the Greek letter Ω (ohm). If your multimeter has multiple resistance ranges, start with the highest one — often labeled 20M or 200M. This protects the meter if the capacitor is shorted.

Touch the red probe to the positive lead of the capacitor and the black probe to the negative lead. On an electrolytic capacitor, the positive lead is longer and the negative lead is shorter; the negative lead also has a stripe printed on the capacitor's body. On a ceramic or film capacitor, the leads are unmarked, so polarity does not matter for this test.

Watch the multimeter display. A working capacitor will show a reading that starts at zero or very low and climbs gradually toward infinity (usually displayed as "OL" for overload). This climbing happens because the capacitor is charging through the multimeter's internal battery. The climb may take a few seconds on large capacitors.

If the reading stays at zero or very low and does not climb, the capacitor is shorted and has failed. If the reading jumps immediately to infinity and never moves, the capacitor is open (broken internally) and has also failed. Either way, the capacitor needs to be replaced.

Measure capacitance if your multimeter has that setting

Many modern multimeters include a capacitance mode, marked with a symbol like µF (microfarads) or nF (nanofarads). This mode measures the actual capacitance value instead of just checking whether the capacitor works. To use it, set the dial to the capacitance setting and touch the probes to the capacitor's leads — polarity does not matter for this measurement.

The display will show a number. Compare this number to the value printed on the capacitor's body. The printed value is usually followed by a tolerance rating, like "10µF ±20%", which means the actual capacitance can be anywhere from 8µF to 12µF and still be considered good. If your measured value falls within that range, the capacitor is working normally.

If the measured value is far outside the tolerance range — for example, you measure 5µF when the capacitor is rated 10µF ±20% — the capacitor is degraded and should be replaced. If the display shows zero or "OL", the capacitor is open and has failed.

Why the reading matters: shorted, open, or good

A shorted capacitor has an internal short circuit and reads zero or very low resistance that does not climb. This is the most common failure mode. A shorted capacitor will draw excessive current from your power supply and can cause other components on the circuit board to overheat or fail.

An open capacitor has a break in its internal structure and reads as infinite resistance immediately. An open capacitor stops working but usually does not damage other components. It simply stops doing its job — filtering noise, storing charge, or blocking DC voltage, depending on where it sits in the circuit.

A good capacitor shows the climbing resistance pattern on the resistance test, or shows a capacitance value within the tolerance range on the capacitance test. A good capacitor is safe to leave in the circuit.

Common mistakes that give you wrong readings

The most common mistake is testing an electrolytic capacitor with the probes reversed. Electrolytic capacitors are polarized, and testing them backwards can give a false reading or even damage the capacitor further. Always put the red probe on the longer lead (positive) and the black probe on the shorter lead (negative).

Another mistake is not waiting long enough for the resistance reading to climb. On a large capacitor (10µF or higher), the climb can take three to five seconds. If you look at the meter too quickly, you might think the capacitor is shorted when it is actually just charging slowly.

Testing a capacitor while it is still connected to the circuit board can also give false readings, because the resistance of other components on the board will interfere with the measurement. If possible, desolder the capacitor or at least disconnect one lead before you test it.

When to replace a capacitor instead of testing it

If a device stopped working and you suspect a capacitor has failed, you do not always need to test it first. Electrolytic capacitors fail predictably — usually after five to ten years of use — and if your device is old and has stopped working, replacing the capacitor is often faster than testing it. Capacitors are inexpensive, usually between 25 cents and two dollars each.

If you are troubleshooting a device that is still partially working, or if you want to confirm that a capacitor is the problem before you order a replacement, then testing makes sense. The resistance mode test takes two minutes and works on any multimeter, so it is worth doing if you already have a meter in your hand.

Frequently Asked Questions

Can I test a capacitor while it is still soldered to the circuit board?

You can try, but the reading will often be wrong because other components on the board are in parallel with the capacitor and will affect the resistance measurement. If the test shows the capacitor is good but the device still does not work, desolder one lead of the capacitor and test it again. This removes the interference from other components.

What does it mean if the multimeter shows "OL" immediately when I touch the probes?

The capacitor is open — it has failed internally and no longer holds a charge. An open capacitor needs to be replaced. This is less common than a shorted capacitor but still a complete failure.

Do I need a special multimeter to test capacitors?

No. Any multimeter with a resistance mode can do the basic shorted-or-open test. A multimeter with a capacitance setting is more useful because it tells you the actual capacitance value, but it is not required. Basic multimeters cost between 10 and 20 dollars and work fine for this test.

Why does the resistance reading climb slowly instead of jumping to a number?

The multimeter's internal battery is charging the capacitor through its probes. As the capacitor charges, its resistance appears to increase. This is normal behavior and actually a sign the capacitor is working. The climb should continue until the reading reaches infinity (displayed as "OL").

Can I test a capacitor that is still powered on?

No. Always turn off the device and unplug it before you test any component. Testing a live circuit can damage your multimeter and shock you. Wait at least five minutes after unplugging to allow capacitors to discharge through the circuit's built-in resistors.