What a multimeter can and cannot tell you about a capacitor
A multimeter can detect some capacitor failures but not all of them. In the most useful test, you set the meter to resistance or ohms mode, touch the probes to the capacitor leads, and watch whether the reading climbs from zero toward infinity. A healthy capacitor will show this rising resistance. A shorted capacitor will stay at zero. A capacitor that is open (broken internally) will show infinite resistance immediately.
What a multimeter cannot do is measure the actual capacitance value or catch a capacitor that has lost some of its ability to store charge but still appears to work. For those tests you need a dedicated capacitance meter or an LCR meter. A multimeter is useful for finding obviously dead capacitors, not for diagnosing weak ones.
Before you test anything, discharge the capacitor. Even a small one can hold enough charge to damage the meter or hurt you. Touch both leads together with an insulated screwdriver, or touch each lead to ground separately. Wait a few seconds to be sure.
Key Takeaways
- Set your multimeter to resistance (ohms) mode and touch the probes to the capacitor leads to see if resistance climbs from zero toward infinity, which indicates a healthy capacitor.
- A capacitor that reads zero ohms is shorted and has failed; one that reads infinite ohms immediately may be open and also failed.
- Always discharge the capacitor before testing by touching both leads together with an insulated tool or touching each lead to ground.
- A multimeter cannot measure actual capacitance value or detect a capacitor that has weakened but still holds some charge.
How to set up the multimeter for the resistance test
Turn off power to the circuit and unplug the device if possible. Remove the capacitor from the circuit board or device so the meter reads only the capacitor, not other components in parallel with it. If the capacitor is soldered in place and you cannot remove it safely, the test will not work reliably because other paths for current will interfere with the reading.
Set the multimeter dial to the resistance setting, usually marked with the Greek letter omega (Ω). If your meter has multiple resistance ranges, start with the highest one — often 20 megohms or higher. Some meters have a dedicated capacitance mode (marked with a capacitor symbol), which is faster and more accurate if your meter has it, but the resistance test works on any meter.
Reading the needle or display as you touch the probes
Touch the red probe to the positive lead of the capacitor and the black probe to the negative lead. Watch the meter immediately. On an analog meter with a needle, the needle should swing from the left (zero ohms) toward the right (higher resistance). On a digital meter, the number should start low and climb higher. This climbing happens because the capacitor is charging through the meter's internal battery.
The needle or number should keep climbing and eventually settle near the highest resistance the meter can measure — often millions of ohms or "infinity" on a digital display. This behavior means the capacitor is holding a charge and is not shorted. If the reading stops climbing and stays at a low number, the capacitor is shorted and has failed. If the reading jumps to infinity instantly without any climb, the capacitor may be open (broken internally) and has also failed.
Reverse the probes and repeat. You should see the same climbing behavior in the opposite direction. This confirms the capacitor is working in both directions.
What different meter readings mean
A reading that climbs steadily and settles high means the capacitor is probably good. The exact final number does not matter much — what matters is that the resistance increased over time, showing the capacitor can charge and hold that charge.
A reading that stays at zero or very close to zero, even after several seconds, means the capacitor is shorted. The two internal plates are touching or nearly touching, and the capacitor cannot hold a charge. This capacitor has failed and should be replaced.
A reading that jumps to infinity (or shows "OL" for overload on a digital meter) instantly without any climb means the capacitor is open. The internal connection is broken, and no current can flow at all. This capacitor has also failed and should be replaced.
A reading that climbs but stops partway and does not reach high resistance may indicate a weak or leaky capacitor. This is harder to diagnose with a multimeter alone, and a capacitance meter would give you a clearer answer. In a working device, a weak capacitor often causes visible problems — flickering, buzzing, or failure to start — before the multimeter shows it clearly.
Why removing the capacitor from the circuit matters
If the capacitor is still soldered to the circuit board, other components connected in parallel with it will provide alternate paths for current. The meter will measure the resistance of those paths, not just the capacitor. This usually makes the reading unreliable or impossible to interpret.
Desoldering a capacitor safely requires a soldering iron, solder wick or a desoldering pump, and some practice. If you are not comfortable doing this, you can sometimes test a capacitor in place by disconnecting one lead — but this only works if you can safely access and lift one lead without damaging the board. Even then, the test is less reliable than testing a fully removed capacitor.
Safety steps before and after testing
Discharge the capacitor before you touch it. Large capacitors in power supplies, audio amplifiers, and old televisions can hold dangerous amounts of charge even when the device is unplugged. Touch both leads together briefly with an insulated screwdriver, or touch each lead to a ground point like the metal chassis. Wait a few seconds, then touch them again to be sure.
After you finish testing, discharge the capacitor again the same way. If you tested a capacitor that was charged, the meter may have charged it during the test, and it could still hold a small charge.
If you are working inside a device with high voltage — like a microwave, old television, or large amplifier — treat every capacitor as dangerous until you have discharged it yourself. Do not rely on the device being unplugged.
When a multimeter test is not enough
A multimeter tells you whether a capacitor is obviously dead (shorted or open), but it does not tell you whether a capacitor has lost capacitance over time. A capacitor might read as "good" on a resistance test but have only half its original capacitance value. In a circuit, this weak capacitor might cause the device to run slowly, produce noise, or fail to start.
If you suspect a weak capacitor, you need a capacitance meter or LCR meter (which measures inductance, capacitance, and resistance). These meters directly measure the capacitance value in farads and can tell you whether the capacitor is within its rated range. They cost more than a basic multimeter but are necessary for accurate diagnosis.
In practice, if a device is not working and you find a capacitor that fails the multimeter test, replacing it will usually fix the problem. If the device still does not work after replacing a capacitor that passed the multimeter test, the capacitor was probably weak, and a capacitance meter would have caught it.
Frequently Asked Questions
Can I test a capacitor while it is still soldered to the board?
You can try, but the result will not be reliable. Other components in parallel with the capacitor will provide alternate current paths, and the meter will measure those paths instead of just the capacitor. For an accurate test, desolder one lead or remove the capacitor entirely. If you cannot safely do that, the test is not worth trusting.
What if the meter needle does not move at all?
On an analog meter, a needle that does not move usually means the capacitor is open (broken internally). On a digital meter, a reading that jumps to infinity or "OL" instantly means the same thing. Either way, the capacitor has failed and should be replaced. Make sure you are using the right probe polarity and that the meter is set to a resistance range, not voltage.
Do I need to discharge the capacitor if the device has been unplugged for a while?
Yes. Even after hours or days unplugged, a large capacitor can hold a charge. The only safe way to know it is discharged is to discharge it yourself with an insulated tool. This takes just a few seconds and prevents damage to the meter or injury to you.
Can a multimeter test capacitors in a microwave?
Microwave capacitors are dangerous and can hold a lethal charge even when unplugged. If you must test one, discharge it very carefully by touching both leads to ground with an insulated screwdriver, then wait several seconds and repeat. Better yet, replace the capacitor without testing it if you suspect it has failed. The cost of a new capacitor is far less than the risk.
What is the difference between a capacitor that reads zero and one that reads infinity?
A capacitor that reads zero ohms is shorted — the two internal plates are touching, and it cannot hold a charge. A capacitor that reads infinity is open — the internal connection is broken, and no current can flow. Both have failed, but they failed in different ways. Either way, the capacitor should be replaced.