The fastest way to test a capacitor

A capacitor is a component that stores electrical charge. When one fails, it can cause a device to stop working, display a black screen, or behave erratically. The most practical way to test one is with a digital multimeter — a handheld tool that measures voltage, resistance, and capacitance. Most modern multimeters have a capacitance setting that reads the value directly in microfarads (µF) or nanofarads (nF).

Before you start, power off and unplug the device completely. If the capacitor is soldered to a circuit board, you may need to desolder it first — if you are not comfortable doing that, a technician can do it for you. If the capacitor is in a removable module or plug-in card, you can test it in place.

The test itself takes about 30 seconds: set your multimeter to the capacitance setting, touch the probes to the capacitor's two leads, and read the value. If the reading is zero, drastically lower than the marked value, or shows "OL" (overload), the capacitor has likely failed.

Key Takeaways

  • A digital multimeter with a capacitance setting is the standard tool for testing capacitors and costs between $15 and $50.
  • The capacitor's marked value (printed on its body) tells you what the reading should be; a reading of zero or far below that value indicates failure.
  • You must power off and unplug the device before testing, and discharge the capacitor by touching a screwdriver across its leads to release stored charge safely.
  • Electrolytic capacitors have polarity (positive and negative leads), so you must touch the red probe to the positive lead and the black probe to the negative lead.
  • If the multimeter shows "OL" or the reading is unstable, the capacitor is likely bad and should be replaced.

What the capacitor's markings tell you

Every capacitor has a value printed or stamped on its body. This value is what you are comparing your multimeter reading against. The value is usually given in microfarads (µF), nanofarads (nF), or picofarads (pF). For example, a capacitor marked "10µF" should read close to 10 microfarads when you test it.

Capacitors also have a tolerance rating — usually printed as a letter or percentage — that tells you how far off the reading can be and still be normal. A tolerance of ±20% means a 10µF capacitor could read anywhere from 8µF to 12µF and still be good. If your reading falls within that range, the capacitor is likely fine. If it is far below the marked value or reads zero, it has failed.

On electrolytic capacitors (the cylindrical ones), you will also see a stripe or marking on one end. That end is the negative lead. The other end is positive. This polarity matters when you test — you must connect the red probe to positive and the black probe to negative, or the reading may be inaccurate.

Setting up your multimeter correctly

Turn your multimeter on and look for the capacitance setting. It is usually marked with a symbol that looks like two parallel lines (the capacitor symbol) or the letters "µF" or "nF". Rotate the dial to that setting. If your multimeter has multiple capacitance ranges (like 2µF, 20µF, 200µF), start with the range closest to the capacitor's marked value. If you are unsure, start with the highest range and work down.

Some older or budget multimeters do not have a capacitance setting. If yours does not, you can still test a capacitor using the resistance setting, but the process is less direct and the results are harder to interpret. A capacitance setting is much more reliable, so if you plan to test capacitors regularly, it is worth upgrading to a multimeter that has one.

The step-by-step testing process

First, discharge the capacitor safely. Even when a device is unplugged, a capacitor can hold a charge that could shock you or damage your multimeter. Touch a screwdriver or wire across both leads of the capacitor for a second or two. You may see a small spark — that is normal and means the charge has been released.

Set your multimeter to the capacitance setting and select the range that matches or exceeds the capacitor's marked value. Touch the red probe to the positive lead of the capacitor (the longer lead on a new capacitor, or the end without the stripe on an electrolytic capacitor). Touch the black probe to the negative lead. Hold the probes steady for a second or two while the meter takes a reading.

Read the value on the display. Compare it to the marked value and its tolerance. If the reading is within the tolerance range, the capacitor is good. If the reading is zero, much lower than marked, or shows "OL" (overload), the capacitor has failed and should be replaced. If the reading is unstable or fluctuates, that also suggests the capacitor is bad.

When a capacitor fails the test

A failed capacitor usually shows one of three signs: a reading of zero, a reading far below the marked value, or an "OL" (overload) message. Any of these means the capacitor is not storing charge properly and should be replaced. In some cases, a capacitor may read correctly but still be failing — this happens when the capacitor is failing intermittently or when the problem is not with capacitance but with its equivalent series resistance (ESR), which a basic multimeter cannot measure.

If you replace a capacitor and the device still does not work, the problem may be elsewhere on the circuit board. A failed capacitor is a common cause of device failure, but it is not the only one. If you are not confident soldering a new capacitor in place, a repair technician can do it for you.

Capacitors you cannot test with a multimeter

Film capacitors and ceramic capacitors can be tested with a multimeter, but the reading may be less stable than with electrolytic capacitors. The needle or display may drift slightly as you watch — this is normal for these types. If the reading is close to the marked value, the capacitor is likely good.

Tantalum capacitors are more sensitive and can be damaged by the voltage that a multimeter applies during testing. If you are testing a tantalum capacitor, use the lowest capacitance range on your multimeter and remove the probes quickly. If you are unsure whether a capacitor is tantalum, check its markings or look it up — tantalum capacitors are usually marked with a "+" sign and are often brown or yellow in color.

Tools and equipment you will need

A digital multimeter with a capacitance setting is the main tool. Basic models with capacitance measurement start around $15 to $25 and are widely available at electronics retailers and online. Mid-range models with more features and better accuracy cost $30 to $60. You do not need an expensive meter for basic capacitor testing.

You will also need a screwdriver or wire to safely discharge the capacitor before testing. If the capacitor is soldered to a circuit board and you want to test it in isolation, you will need a soldering iron and solder sucker or desoldering braid to remove it. If you are not comfortable soldering, you can test the capacitor while it is still on the board — the reading may be affected by other components, but a completely failed capacitor will usually still show zero or far below its marked value.

Frequently Asked Questions

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

Yes, but the reading may be affected by other components connected to it. If the capacitor reads zero or far below its marked value, it is almost certainly bad. If the reading is close to the marked value, the capacitor is probably good, but other components on the board could still be causing the problem.

What does "OL" mean on my multimeter when testing a capacitor?

OL stands for "overload" and usually means the capacitor is open (broken) or the range you selected is too low for the capacitor's value. Try selecting a higher capacitance range. If you still see OL on the highest range, the capacitor has likely failed.

Do I need to discharge a capacitor before testing it?

Yes. Even when a device is unplugged, a capacitor can hold a dangerous charge. Touch a screwdriver across both leads for a second to release the charge safely. You may see a small spark — that is normal and means the capacitor is discharging.

Why does my multimeter reading keep changing when I test a capacitor?

Some capacitor types, especially film and ceramic capacitors, have readings that drift slightly as the meter measures them. This is normal. If the reading stabilizes near the marked value, the capacitor is likely good. If it stays at zero or far below the marked value, the capacitor has failed.

Can a capacitor pass a multimeter test but still be bad?

Yes, though it is uncommon. A capacitor can read correctly for capacitance but fail due to high equivalent series resistance (ESR), which a basic multimeter cannot measure. If you replace a capacitor that tested good and the device starts working, the capacitor was likely failing in a way the multimeter could not detect.