What a multimeter can and cannot tell you about a capacitor
A multimeter can detect whether a capacitor is completely dead, but it cannot measure the actual capacitance value accurately in most cases. If you set your multimeter to capacitance mode (usually marked with a symbol that looks like two parallel lines), you can get a rough reading on some capacitors—but the result is often unreliable, especially for capacitors already installed in a circuit. For a definitive test, you need either a dedicated capacitance meter or a multimeter with a strong capacitance function, which costs more than a basic model.
The most useful thing a standard multimeter tells you is whether a capacitor is shorted (dead) or open (broken). A shorted capacitor reads zero or near-zero resistance. An open capacitor reads infinite resistance. A working capacitor will show a brief resistance spike when you first touch the probes to it, then the reading climbs toward infinity as the capacitor charges. That spike is what you are looking for.
Key Takeaways
- Set your multimeter to resistance mode (ohms), not capacitance mode, for the most reliable test on a capacitor you suspect is faulty.
- A working capacitor will show a brief resistance spike when you first connect the probes, then climb toward infinite resistance as it charges.
- A shorted capacitor reads near-zero resistance and stays there; an open capacitor reads infinite resistance immediately.
- Always discharge the capacitor first by touching a screwdriver across its leads, and never test a capacitor while it is still connected to a powered circuit.
How to safely prepare a capacitor for testing
Before you touch a multimeter probe to any capacitor, you must discharge it. A charged capacitor can hold voltage even after the device is unplugged, and that voltage can damage your multimeter or injure you. The safest way is to use an insulated screwdriver: touch the metal shaft across both capacitor leads at the same time. You will see a small spark—that is the capacitor discharging. Wait a second, then do it again to make sure.
Next, remove the capacitor from the circuit board if possible. Testing a capacitor while it is still soldered in place gives false readings because the rest of the circuit interferes with the measurement. If you cannot desolder it, you can still test it, but the result is less reliable. Let the capacitor sit for a few seconds after discharge before you begin the test.
Testing with resistance mode (the most common method)
Set your multimeter dial to the resistance setting, usually marked with the Greek letter omega (Ω). Start on the highest resistance range available—often 20 megohms or higher. This protects your meter from damage if the capacitor is shorted.
Touch the red probe to the positive lead of the capacitor and the black probe to the negative lead. Watch the display. In the first second or two, the resistance will drop sharply—this is the capacitor charging through the meter. Then the reading will climb steadily toward infinity (usually shown as "OL" or "1" on the display, depending on your meter). This climbing behavior means the capacitor is good.
If the resistance stays at zero or near-zero and does not climb, the capacitor is shorted and should be replaced. If the resistance jumps immediately to infinity and never dips, the capacitor is open (broken) and should also be replaced. Reverse the probe positions and repeat the test. A good capacitor will show the same climbing pattern in both directions.
Testing with capacitance mode (if your meter has it)
Some multimeters have a dedicated capacitance mode, marked with a symbol like two parallel lines or the letter F (for farads). If your meter has this, set the dial to capacitance and select the range closest to the capacitor's rated value. The rated value is printed on the capacitor itself, usually in microfarads (µF) or nanofarads (nF).
Touch the probes to the capacitor leads and wait for the reading to stabilize. A good capacitor will show a value close to its rated capacitance—usually within 10 to 20 percent. If the reading is zero or far below the rated value, the capacitor is faulty. If the reading is infinite or the meter shows an error, the capacitor is open.
Capacitance mode is faster and more direct than resistance mode, but it is less reliable on older or cheaper multimeters. If your capacitance reading seems wrong, fall back to the resistance test to confirm.
What different readings actually mean
A climbing resistance reading (starting low, rising toward infinity) means the capacitor is working. This is the most important sign. The climb happens because the capacitor is charging through the meter's internal resistance, and as it charges, it blocks current flow, which the meter reads as increasing resistance.
A stuck-at-zero resistance reading means the capacitor is shorted internally. The two plates inside are touching, so current flows freely with no resistance. This capacitor cannot store charge and must be replaced.
A stuck-at-infinity reading (shown as "OL" or "1") means the capacitor is open—one of the internal connections is broken. No current can flow at all. This capacitor is also dead and needs replacement.
A capacitance reading far below the rated value (in capacitance mode) means the capacitor is degraded. It may still work in some circuits, but it is not reliable. In audio equipment or power supplies, a degraded capacitor often causes hum, distortion, or failure to start.
Common mistakes that give false results
Testing a capacitor while it is still powered or connected to a live circuit is the most common error. The circuit's voltage interferes with the meter's measurement and gives a false reading. Always unplug the device first, wait 30 seconds, and discharge the capacitor before testing.
Touching the capacitor leads with your fingers while testing can also skew the result. Your skin has resistance, and that resistance becomes part of the circuit the meter is measuring. Hold the capacitor by its body, not its leads, or use a small clip to hold the probes in place.
Using the wrong meter range is another source of error. If you set the resistance range too low (like 200 ohms), a good capacitor may read as shorted because the meter cannot see the charging curve. Always start on the highest resistance range and work down if needed.
When to replace a capacitor versus when to keep testing
If the resistance test shows a clear climbing pattern from low to high, or if the capacitance reading is within 10 to 20 percent of the rated value, the capacitor is good. Stop testing and reinstall it if you removed it.
If the reading is stuck at zero, stuck at infinity, or far below the rated value, replace the capacitor. Do not assume it might work anyway. A failed capacitor in a power supply or audio circuit often causes damage to other components, so it is cheaper to replace it now than to repair the whole device later.
If the reading is borderline—say, 50 percent of the rated value—and the device is working fine, you can leave it in place. Capacitors degrade over time, and a slightly weak capacitor may still function. But if the device is misbehaving (humming, not starting, cutting out), replace it anyway.
Frequently Asked Questions
Can I test a capacitor while it is still in the circuit?
You can, but the result is unreliable because the rest of the circuit interferes with the measurement. Desoldering the capacitor takes 10 minutes and gives you a definitive answer. If desoldering is not possible, test it in place, but confirm the result by testing it again after you remove it.
What does it mean if the resistance reading does not move at all?
If the reading stays at zero, the capacitor is shorted. If it stays at infinity (OL), the capacitor is open. Either way, it is dead. A good capacitor always shows movement—a dip and then a climb—in the first few seconds.
Why does my capacitance reading not match the number printed on the capacitor?
Capacitors have a tolerance, usually ±10 to ±20 percent, printed on the body. A reading within that range is normal. If the reading is far outside the tolerance, the capacitor is degraded. Also, some multimeters have weak capacitance circuits and give inaccurate readings; the resistance test is more reliable on these meters.
Is it safe to test a capacitor with my hands near the leads?
No. Your skin resistance becomes part of the circuit and throws off the reading. Also, if the capacitor is not fully discharged, you could get a shock. Hold the capacitor by its body or use a clip to hold the probes. Always discharge it first with an insulated screwdriver.
Can a multimeter damage a capacitor during testing?
No. The voltage and current from a multimeter are too small to harm a capacitor. The only risk is to the multimeter itself if you test a shorted capacitor on a low resistance range—that is why you always start on the highest range.