The fastest way to test a capacitor

The most practical way to check a capacitor is with a digital multimeter set to capacitance mode. Most multimeters sold today have this function built in. You disconnect the capacitor from the circuit, set the dial to the capacitance setting (usually marked with a symbol that looks like two parallel lines), touch the probes to the capacitor's leads, and read the value on the screen. If the reading is close to the capacitor's rated value printed on its body, the capacitor is likely working. If the reading is zero, extremely high, or shows an error, the capacitor has failed.

This method works for most common capacitors you will encounter in consumer electronics. It takes about 30 seconds per capacitor and requires no special knowledge beyond knowing where the capacitance dial is on your meter. The main limitation is that some multimeters do not include a capacitance function — usually the cheaper models under $20 — so check your meter's dial before you start.

Key Takeaways

  • A digital multimeter with capacitance mode is the standard tool for testing capacitors, and the test takes less than a minute.
  • Disconnect the capacitor from the circuit before testing, and if it is large, discharge it first by touching a screwdriver across both leads to avoid electric shock.
  • A healthy capacitor reads close to its rated value on the meter; a reading of zero, infinity, or an error message means the capacitor has failed.
  • Electrolytic capacitors (the cylindrical ones with a stripe) are more prone to failure than film or ceramic capacitors and should be tested if a device stops working.

How to set up your multimeter for the test

Start by turning off and unplugging the device the capacitor is in. Locate the capacitor you want to test — it will be a small component on the circuit board, usually cylindrical (electrolytic), disc-shaped (ceramic), or rectangular (film). If you cannot identify it, look for a component with two leads and a value printed on it like "10µF" or "100nF".

If the capacitor is soldered to the circuit board, you will need to desolder it first using a soldering iron or desoldering pump. If it has wire leads you can simply pull out, remove it from the board. For large electrolytic capacitors, discharge any stored charge by touching a screwdriver or wire across both leads for a second — this prevents a shock when you handle it.

Turn your multimeter on and locate the dial. Look for a symbol that resembles two parallel lines (the capacitor symbol) or text that says "µF", "nF", or "pF". Rotate the dial to that setting. If your meter has multiple capacitance ranges (like 2µF, 20µF, 200µF), start with the highest range and work down if needed.

Taking the measurement

Touch the red probe to one lead of the capacitor and the black probe to the other lead. The order does not matter for most capacitors, but for electrolytic capacitors (which have a positive and negative lead marked on the body), touching red to positive and black to negative is the correct way. Hold the probes steady for two to three seconds while the meter takes the reading.

Read the number on the screen. The capacitor's rated value is printed on its body — for example, "47µF" means 47 microfarads. A healthy capacitor will read within about 10 to 20 percent of this value. So a 47µF capacitor might read anywhere from 40µF to 54µF and still be good. If the reading is significantly lower, much higher, or shows "OL" (overload) or an error, the capacitor has likely failed.

What different readings mean

A reading close to the rated value — within the tolerance range printed on the capacitor — means the capacitor is functioning normally. Most capacitors have a tolerance of ±10% or ±20%, which is printed somewhere on the component itself. If your meter shows a value within that range, the capacitor is good.

A reading of zero or very close to zero means the capacitor is shorted internally and has failed. A reading of "OL" (overload) or infinity means the capacitor is open internally and has also failed. Either way, the capacitor needs to be replaced. A reading that is significantly lower than the rated value — say, half the expected value — suggests the capacitor is degrading and may fail soon, especially if the device is showing symptoms like slow startup, dimming, or buzzing sounds.

If your meter shows a reading but it is wildly different from the rated value — for example, a 10µF capacitor reading 500µF — the capacitor has failed. This sometimes happens with electrolytic capacitors that have aged or been exposed to heat.

When you cannot use a multimeter

Some older or very cheap multimeters do not have a capacitance function. If your meter's dial does not show a capacitance symbol or setting, you have a few alternatives. The simplest is to borrow or purchase a meter that does have this function — a basic digital multimeter with capacitance mode costs $15 to $30 and is useful for many other tests.

If you cannot access a meter with capacitance mode, you can perform a visual inspection instead. Look for signs of physical damage: a bulging or leaking top on an electrolytic capacitor, burn marks, or a cracked body. These are reliable signs of failure. You can also test by substitution — remove the suspected bad capacitor and solder in a new one of the same value, then power on the device and see if it works. This is more time-consuming but works when you do not have a meter.

Testing capacitors still connected to a circuit

Ideally, you should desolder the capacitor before testing it, because other components on the circuit board can affect the reading and give you a false result. However, if you want to test in-circuit first to narrow down the problem, you can try — just know that the reading may not be accurate.

Set your multimeter to capacitance mode and touch the probes to the capacitor's leads while it is still soldered in place. If the reading is zero or "OL", the capacitor is definitely bad and you can proceed to desolder it. If the reading looks normal but the device is still not working, desolder the capacitor and test it again to confirm, because the circuit board may have been masking the problem.

Frequently Asked Questions

Do I need to discharge a capacitor before testing it?

Only if it is large and has been powered recently. Small capacitors in consumer electronics hold very little charge. Large electrolytic capacitors in power supplies or audio equipment can hold enough charge to cause a painful shock, so touch a screwdriver across both leads for a second before handling. If you are unsure, discharge it anyway — it takes five seconds and is safer.

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

Yes, occasionally. A capacitor can fail under load — meaning it works fine when sitting on a bench but fails when power flows through it. If your meter shows a good reading but the device still does not work, the capacitor may be the problem anyway. Test by substitution: replace it with a new one of the same value and see if the device works.

What is the difference between µF, nF, and pF?

These are units of capacitance. µF (microfarads) is the largest, nF (nanofarads) is 1,000 times smaller, and pF (picofarads) is 1,000 times smaller still. A 1µF capacitor equals 1,000nF or 1,000,000pF. Your multimeter dial usually has separate ranges for each, so match the unit on the capacitor to the range on your meter.

Why do electrolytic capacitors fail more often than other types?

Electrolytic capacitors use a chemical paste inside that dries out over time, especially when exposed to heat. They typically last 5 to 20 years depending on temperature and usage. Ceramic and film capacitors are more stable and can last 50+ years. If a device is old or runs hot, electrolytic capacitors are usually the first components to fail.

What should I do if my multimeter does not have a capacitance setting?

You can look for physical damage on the capacitor — bulging, leaking, or burn marks are signs of failure. You can also test by substitution: remove the capacitor and solder in a new one of the same value, then power on the device. If it works, the old capacitor was bad. Otherwise, consider purchasing a basic multimeter with capacitance mode for $15 to $30.