What a multimeter tells you about a capacitor

A multimeter can tell you whether a capacitor is completely dead, working normally, or partially failed — but it cannot measure the exact capacitance value the way a dedicated capacitor tester can. Most multimeters have a capacitance setting (marked with a symbol that looks like two parallel lines) that reads the charge a capacitor holds. If your multimeter does not have this setting, you can still test a capacitor using the resistance mode, though the results are less precise.

The test takes about two minutes and requires you to safely discharge the capacitor first, set the multimeter to the right mode, and touch the probes to the capacitor's leads. A reading close to the marked value means the capacitor is probably working. A reading of zero or infinity usually means it has failed.

This test works best on capacitors you have removed from a circuit. Testing a capacitor while it is still soldered to a board can give false readings because other components in the circuit interfere with the measurement.

Key Takeaways

  • Always discharge a capacitor before testing it by touching a screwdriver across both leads — a charged capacitor can deliver a painful shock.
  • Use the capacitance mode (marked with two parallel lines) on your multimeter if it has one, as this gives the most accurate reading.
  • A reading within 10 to 20 percent of the marked value usually means the capacitor is working; a reading of zero or infinity means it has failed.
  • Remove the capacitor from the circuit before testing, because other components can interfere with the reading.
  • If your multimeter has no capacitance mode, you can use the resistance mode as a rough test, though the results are less reliable.

Discharge the capacitor safely before you touch it

A capacitor stores electrical charge even after power is turned off. If you touch both leads at once, that charge will discharge through your body, which can cause a painful shock or even damage to your heart if the capacitor is large. Discharging it first takes ten seconds and eliminates this risk.

Use an insulated screwdriver or a wire with an insulated handle. Touch the metal tip across both leads of the capacitor at the same time, holding it there for a few seconds. You may see a small spark — this is normal and means the capacitor had a charge. If there is no spark, the capacitor was already discharged or is completely dead.

After discharge, you can safely handle the capacitor and test it with your multimeter.

Set your multimeter to capacitance mode

Look at the dial or menu on your multimeter and find the setting marked with a symbol that looks like two parallel horizontal lines (this is the capacitance symbol). The setting is often labeled with a "C" and may have different ranges, such as 2000 µF, 200 µF, or 20 µF. Start with the highest range available — if the reading is too low to display, switch to a lower range and test again.

Some multimeters have a digital display with a menu button instead of a dial. If yours does, press the menu or mode button until you see "Capacitance" or "CAP" on the screen, then select the appropriate range.

Once the multimeter is set to capacitance mode, it is ready to measure. The probes do not need to be connected to power — the multimeter generates a small test signal internally.

Touch the probes to the capacitor leads and read the value

Hold the capacitor steady with one hand. With the other hand, touch the red probe to the positive lead (usually marked with a stripe or longer leg) and the black probe to the negative lead. Hold both probes in place for two to three seconds while the multimeter takes the reading.

Look at the display. The number shown should be close to the value printed on the capacitor's body — for example, if the capacitor is marked "100 µF", the reading should be somewhere between 80 and 120 µF. A reading within 10 to 20 percent of the marked value is normal and means the capacitor is working.

If the reading is exactly zero, the capacitor is open (broken internally). If the reading is infinity or shows "OL" (overload), the capacitor is shorted (the internal plates are touching). Either result means the capacitor has failed and needs replacement.

What to do if your multimeter has no capacitance mode

Older or budget multimeters sometimes lack a capacitance setting. You can still perform a rough test using the resistance mode, though the result is less reliable. Set the dial to the highest resistance range (usually 20 MΩ or higher). Touch the red probe to the positive lead and the black probe to the negative lead.

When you first touch the probes, the resistance reading will drop sharply, then climb back toward infinity over the next few seconds. This climbing needle (or rising number on a digital display) shows the capacitor charging up through the multimeter's internal battery. If the resistance stays at zero or never changes, the capacitor is likely shorted. If it stays at infinity and never moves, the capacitor is likely open.

This test is not precise — it only tells you whether the capacitor is completely dead or possibly working. For a definitive reading, you would need a dedicated capacitor tester or a multimeter with a capacitance mode.

Common mistakes that give false readings

Testing a capacitor while it is still soldered to the circuit board is the most common source of error. Other components in the circuit can conduct current and interfere with the measurement, making a good capacitor look bad or vice versa. Always desolder or remove the capacitor from the board first.

Touching the capacitor leads with your bare fingers while testing can also affect the reading, because your skin conducts electricity. Hold the capacitor by its body or use a small clip to hold it steady, and keep your fingers away from the leads.

If you forget to discharge the capacitor before testing, you risk a shock, but you will not damage the multimeter. However, the shock itself is reason enough to make discharge your first step every time.

When a capacitor test result means replacement

If the multimeter reading is within 10 to 20 percent of the marked value, the capacitor is working and does not need replacement. If the reading is zero, infinity, or nowhere near the marked value, the capacitor has failed and should be replaced with one that has the same capacitance value (measured in microfarads, or µF) and the same voltage rating (marked as "V" on the body).

When you order a replacement, match both numbers exactly. A capacitor marked "100 µF 25V" is not the same as one marked "100 µF 50V" — the voltage rating matters for safety and performance. If you cannot find the exact match, a capacitor with a higher voltage rating will work, but a lower voltage rating will not.

If you are unsure whether a capacitor has failed or whether your multimeter is working correctly, you can test a capacitor you know is good (from a working device) to compare the readings. This confirms that your multimeter is functioning properly.

Frequently Asked Questions

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

You can, but the reading will often be wrong because other components in the circuit conduct current and interfere with the measurement. For an accurate test, remove the capacitor from the board first. If you cannot desolder it, a reading that is far from the marked value is still a sign the capacitor may have failed.

What does it mean if the multimeter shows zero?

A reading of zero means the capacitor is open — the internal connection is broken and it cannot hold a charge. The capacitor has failed and needs replacement. This is different from a shorted capacitor, which shows infinity or overload.

Is it safe to test a large capacitor?

Large capacitors can store enough charge to cause serious injury. Always discharge the capacitor first by touching an insulated screwdriver across both leads. Once discharged, testing with a multimeter is safe — the multimeter itself uses only a tiny test signal.

Why does the reading change each time I test the same capacitor?

Small variations in readings are normal — capacitors naturally drift slightly with temperature and age. If the reading stays within 10 to 20 percent of the marked value, the capacitor is still working. If the reading jumps wildly or drops to zero, the capacitor is failing.

What if the capacitor has no markings showing its value?

The multimeter will still show you a reading, but you will not know whether it is correct without knowing the intended value. If the capacitor is from a working device, you can compare it to an identical part from another unit. Otherwise, a capacitor tester or the original schematic for the device is your best option.