A capacitor stores electrical charge, and you can test whether it still works by measuring that charge with a multimeter

A capacitor is a component that holds electrical energy temporarily, like a tiny rechargeable battery. When a capacitor fails, it either stops holding charge or leaks it away. You can test whether a capacitor is working by using a multimeter — a handheld meter that measures voltage, resistance, and other electrical properties. The test takes about a minute and tells you whether the capacitor is good, weak, or dead.

The method depends on the capacitor's size. Small capacitors (under 10 microfarads) show up on a multimeter's resistance or capacitance setting. Larger capacitors need a different approach because they hold too much charge for a standard meter to measure safely. This guide covers both.

Key Takeaways

  • A multimeter set to resistance or capacitance mode can test small capacitors in seconds without removing them from the circuit.
  • Larger capacitors need to be discharged first by touching a screwdriver across their leads, or they can damage the multimeter or shock you.
  • A good capacitor shows steady resistance that climbs gradually, or a capacitance reading close to the number printed on the component.
  • A failed capacitor shows zero resistance, infinite resistance, or a capacitance reading far below what the label says.
  • If you are not comfortable working inside electronics, testing a capacitor is one of the safest checks you can do — the risk is low if you discharge large capacitors first.

Discharge the capacitor before you touch it

Before testing any capacitor larger than a few microfarads, you must remove the electrical charge it is holding. A charged capacitor can shock you or damage your multimeter. The discharge takes five seconds and is the most important safety step.

Turn off and unplug the device. Wait at least one minute for the capacitor to lose most of its charge on its own. Then 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 may see a small spark — that is normal and means the capacitor had charge. If there is no spark, the capacitor was already discharged. Do this even if you think the device has been off for hours, because some capacitors hold charge for a long time.

Test a small capacitor with the resistance setting

Small capacitors (typically marked under 10 microfarads, or µF) can be tested while still soldered to the circuit board. Set your multimeter to the resistance setting, usually marked with the Greek letter omega (Ω). Touch one probe to each lead of the capacitor.

A good capacitor shows a resistance reading that starts low and climbs toward infinity over a few seconds. You will see the number rise on the display as the capacitor charges through the multimeter's battery. This climbing needle or rising number is the sign of a working capacitor. A failed capacitor shows zero resistance (a short circuit) or stays at infinity without climbing. If the reading does not move or stays stuck at one number, the capacitor is bad.

Test a small capacitor with the capacitance setting

Many modern multimeters have a capacitance setting, marked with the letter C and a curved line. This setting measures the capacitor's actual storage capacity in microfarads (µF) or nanofarads (nF). Set the dial to capacitance mode and touch one probe to each lead.

The meter displays a number. Compare it to the number printed on the capacitor's body. A good capacitor reads within about 20 percent of the marked value — so a capacitor marked 100 µF should read between 80 and 120 µF. A reading far below the marked value, or zero, means the capacitor has failed. If your multimeter does not have a capacitance setting, the resistance test above works just as well.

Test a large capacitor by discharging and measuring voltage

Large capacitors (10 microfarads and above) hold too much charge for a standard multimeter to measure safely. Instead, you test them by watching how they discharge. After discharging the capacitor with a screwdriver as described above, set your multimeter to the DC voltage setting (marked V with a straight line, not a wavy one).

Touch the probes to the capacitor's leads. A good capacitor shows a voltage reading that slowly drops toward zero over several seconds. A failed capacitor shows zero voltage when ready, or the voltage does not drop at all. The voltage drop is the capacitor releasing the charge you just gave it when you touched the screwdriver across its leads — a working capacitor holds that charge and releases it slowly, while a dead one cannot hold anything.

Know when a capacitor is too weak to replace

A capacitor that reads low but not zero — say, 60 µF when it should be 100 µF — is weak but not completely failed. Whether you need to replace it depends on what the device does. In a power supply or audio amplifier, a weak capacitor can cause noise, dimming, or distortion. In a motor or compressor, a weak capacitor may not provide enough starting torque and the motor may not turn on.

If the device is working fine, a weak capacitor may not need replacement yet. If the device is misbehaving — a speaker crackling, a motor struggling to start, a light flickering — a weak capacitor is worth replacing even if it has not failed completely. Capacitors are cheap (usually under five dollars) and straightforward to swap out once you know which one is the problem.

Understand what causes capacitor failure

Capacitors fail for three main reasons: age, heat, and overvoltage. Electrolytic capacitors (the cylindrical ones with a stripe down the side) dry out over years, especially if the device runs hot. A capacitor rated for 85 degrees Celsius will fail faster if it sits next to a heat source. Overvoltage — from a power surge or a failed component upstream — can puncture the capacitor's insulation and cause an when ready short circuit.

When a capacitor fails, it often bulges at the top or leaks a brown or white crusty substance. If you see either sign, the capacitor is definitely bad and needs replacement. A capacitor that looks normal but fails the multimeter test is also bad, even though the reason is not visible.

Frequently Asked Questions

Can I test a capacitor while it is still in the circuit?

Yes, for small capacitors under 10 microfarads. Larger capacitors can give false readings because other components in the circuit affect the measurement. If the test shows the capacitor is bad, you can be confident. If it shows the capacitor is good but the device is still broken, remove the capacitor and test it alone to rule out circuit interference.

What if the multimeter shows a very high resistance that does not climb?

That usually means the capacitor is open — the internal connection is broken. An open capacitor cannot hold or release charge, so it is as useless as a short-circuited one. Replace it.

Is it dangerous to test a capacitor?

The main risk is shock from a charged large capacitor. If you discharge it first with an insulated screwdriver, the risk drops to nearly zero. The multimeter itself is not harmed by testing a capacitor, as long as you use the correct setting and the capacitor is discharged.

Why does the multimeter reading climb when I test with the resistance setting?

The multimeter's battery sends a small current through the capacitor to measure resistance. A working capacitor charges up from that current, and as it charges, the resistance appears to rise. This climbing is the proof that the capacitor can store charge.

Can a capacitor test good on a multimeter but still be bad?

Rarely. A multimeter test catches most failed capacitors. The one exception is a capacitor that fails only under load — when current is actually flowing through the device. If a capacitor tests good but the device still misbehaves, the problem is likely elsewhere, not the capacitor.