What a multimeter can and cannot tell you about a capacitor
A multimeter can detect whether a capacitor is completely dead or shorted, but it cannot measure the actual capacitance value accurately on most meters. The reason: a standard multimeter applies a small voltage to test the capacitor, while the capacitor's real job is to store charge at the voltage your circuit actually uses. A capacitor might read "good" on a multimeter but fail in your circuit, or fail on the meter but work fine where it sits.
If you need to know the exact capacitance value, you need a meter with a dedicated capacitance mode — many modern multimeters have one. If you just need to know whether the capacitor is shorted or completely open, the resistance mode works. This guide covers both approaches.
Key Takeaways
- A multimeter's resistance mode can tell you if a capacitor is shorted (reads near zero ohms) or open (reads infinite), but not whether it holds the right amount of charge.
- Capacitors must be fully discharged before testing, or the meter reading will be wrong and you risk damaging the meter.
- If your multimeter has a capacitance mode, use that instead of resistance mode — it gives you the actual value in microfarads or nanofarads.
- A capacitor that reads good on a multimeter can still fail in the circuit, so multimeter testing is one step in diagnosis, not the final answer.
Discharge the capacitor completely before you touch it
A charged capacitor can deliver a shock and can damage your multimeter. Before any test, you must remove all stored charge. The safest way is to use an insulated screwdriver or a discharge tool: touch one end of the screwdriver to one capacitor lead, then touch the other end to the other lead. You will see a small spark — that is the charge leaving. Do this once, wait a few seconds, then do it again to be sure.
If the capacitor is still in the circuit, turn off and unplug the device first. If the capacitor is large (over 10 microfarads), discharge it twice. If you are not sure whether it is discharged, use a multimeter set to voltage mode and touch the leads to the capacitor terminals — if the voltage reads zero, it is safe.
Testing with resistance mode (works on any multimeter)
Set your multimeter dial to the resistance setting, usually marked with the Greek letter omega (Ω). The exact position depends on your meter, but it is typically grouped with other test modes. Start on the highest resistance range if your meter has multiple ranges.
Touch the red probe to one capacitor lead and the black probe to the other. Watch the needle or digital display. A good capacitor will show a brief movement toward zero ohms, then climb back toward infinity (or show "OL" on a digital meter, meaning "open line"). This happens because the capacitor is charging from the meter's battery. If the needle stays at zero or near zero, the capacitor is shorted. If it does not move at all and stays at infinity, the capacitor is open and dead.
Reverse the probes and repeat. You should see the same brief dip and climb. If one direction shows a short and the other does not, the capacitor is damaged. If both directions show infinity with no movement, the capacitor is open.
Testing with capacitance mode (more accurate)
If your multimeter has a capacitance mode — usually marked with a symbol that looks like two parallel lines or the letters "F" with a subscript — use that instead. Set the dial to capacitance and choose the range that matches the capacitor you are testing. If the capacitor is marked 10 microfarads (µF), start on the 20 µF or 200 µF range. If it is marked in nanofarads (nF), use the nanofarad range.
Touch the red probe to the positive lead (if marked) and the black probe to the negative lead. The meter will display a number. Compare it to the value printed on the capacitor body. A reading within 10 to 20 percent of the marked value is usually acceptable — a 10 µF capacitor reading 9 to 11 µF is fine. A reading of zero or far below the marked value means the capacitor is failing.
If your meter shows "OL" or does not settle on a number, the capacitor is open. If it shows a value but the capacitor is visibly swollen, leaking, or burned, replace it anyway — the meter cannot detect age-related failure.
What to do when the test shows a problem
If the capacitor reads shorted (near zero ohms in resistance mode, or zero in capacitance mode), it must be replaced. A shorted capacitor can damage other parts of the circuit and may overheat or catch fire.
If the capacitor reads open (infinite ohms, or zero in capacitance mode), it is also dead and must be replaced. An open capacitor stops doing its job — it cannot filter, smooth, or block voltage anymore.
If the capacitor reads within range on the multimeter but the device still does not work, the capacitor may be failing under load. This is the limitation of multimeter testing: the meter applies a tiny voltage in a controlled way, but your circuit applies real voltage under real conditions. The capacitor might fail only when it is actually working. In this case, you can try replacing it anyway, or use an ESR meter (equivalent series resistance meter) for a more detailed test.
Common mistakes that give wrong readings
Touching the capacitor leads with your bare fingers while testing changes the reading because your body adds capacitance. Hold the capacitor by the body or the insulation, not the leads. If you are testing a capacitor still soldered to a board, make sure the board is powered off and fully discharged.
Testing a capacitor that is not fully discharged will give a false reading and can damage the meter. Always discharge first. If you test the same capacitor twice in a row without discharging between tests, the second reading will be wrong because the meter's battery has not had time to fully charge it again — wait 10 seconds between tests.
Using the wrong range on a multimeter with multiple ranges will show "OL" even on a good capacitor. If you are testing a 10 µF capacitor and you set the meter to the 2 µF range, it will read out of range. Start high and work down.
When multimeter testing is not enough
A multimeter tells you whether a capacitor is shorted or completely open, but it does not tell you whether the capacitor is aging, whether it holds charge long enough, or whether it will fail under the voltage and temperature of your actual circuit. If a device has intermittent problems and the capacitor reads good on a multimeter, the capacitor might still be the cause.
For a more complete test, an ESR meter measures the internal resistance of the capacitor — a high ESR reading means the capacitor is aging even if it still holds the right capacitance. An LCR meter measures capacitance, inductance, and resistance all at once and is more accurate than a standard multimeter. These tools are more expensive and less common, but they catch failures that a multimeter misses.
Frequently Asked Questions
Can I test a capacitor while it is still soldered to the circuit board?
You can, but the reading may be wrong because other components on the board affect the measurement. Disconnect the capacitor from the board first if possible. If you must test it in place, discharge the entire board first and be aware that the reading might not be accurate.
What does it mean if the capacitor reads good on the multimeter but the device still does not work?
The capacitor may be failing under the actual voltage and temperature of your circuit, even though it passes the multimeter test. Try replacing it. Alternatively, the problem may be something else entirely — a multimeter test on one component does not rule out other failures.
How do I know which lead is positive on a capacitor?
On electrolytic capacitors, the longer lead is positive and the shorter lead is negative. On film or ceramic capacitors, there is usually no polarity marking. For testing purposes, polarity does not matter on a multimeter — you can touch either lead to either probe.
Can a capacitor be partially bad?
Yes. A capacitor can lose capacitance over time (aging), develop high internal resistance (ESR), or fail only under certain voltages or temperatures. A multimeter will not catch all of these problems — it only detects complete shorts and opens.
What should I do if the multimeter sparks when I touch the capacitor leads?
The capacitor was not fully discharged. Stop immediately and discharge it again using an insulated screwdriver. A spark means there was still significant charge stored, which could damage the meter or injure you.