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A capacitor can be tested with a digital multimeter by measuring its capacitance, checking its charging behavior in resistance mode, and inspecting it for physical damage. Disconnect all power, discharge the capacitor safely, verify the remaining voltage, and isolate at least one terminal before measuring. This guide explains each step, how to interpret the reading, and why a normal capacitance value does not rule out high ESR or leakage.
Figure 1. Testing a Capacitor with a Digital Multimeter in Capacitance Mode
Do not test or discharge capacitors in microwave ovens, camera flashes, CRT equipment, HVAC systems, mains power supplies, electric vehicles, or other high-energy equipment unless you are trained and have the correct service procedure and safety equipment.
A capacitor can retain electrical energy even after the equipment is switched off. This is especially important with large electrolytic capacitors, power-supply capacitors, motor capacitors, and high-voltage circuits, where the stored energy can cause electric shock, burns, or damage to the meter and circuit. [3,5]
Figure 2. Capacitor Discharging on a Circuit Board
Before testing:
• Disconnect all power sources. Unplug the equipment and disconnect batteries, external power supplies, or other energy sources.
• Do not assume the capacitor is discharged. Some capacitors can remain charged for a significant time after power is removed.
• Use a controlled discharge method. Follow the equipment manufacturer's service procedure when available. For higher-energy capacitors, use a properly rated discharge resistor or approved discharge tool rather than directly shorting the terminals. [3,5]
• Avoid touching exposed terminals. Use insulated tools and keep your hands away from conductive parts during the discharge process.
• Verify the voltage before testing. Use the appropriate AC or DC voltage range to verify that the circuit power is off. After controlled discharge, measure directly across the capacitor and confirm that the residual voltage is near zero or below the equipment manufacturer’s specified safe level. [2,3]
• Check the voltage again if necessary. Some capacitors can show voltage recovery after discharge because of dielectric absorption, so recheck before handling or reconnecting the component. [5]
Do not proceed with capacitance or resistance testing until the capacitor has been safely discharged and the remaining voltage has been verified with the multimeter. [2,3]
Capacitance mode is the preferred multimeter method because it measures the capacitor’s capacitance directly. As shown in Figure 1, the multimeter probes are connected to the capacitor terminals while the meter is set to capacitance mode. After completing the required safety steps, follow these steps: [2,3]
• Isolate the capacitor. Disconnect at least one terminal from the circuit so other components do not affect the measurement. [3]
• Select capacitance mode. Set the multimeter to the capacitance function, usually marked with a capacitor symbol or units such as pF, nF, or µF.
• Connect the probes. Place the probes across the capacitor terminals. For a polarized capacitor, connect the red probe to the positive terminal and the black probe to the negative terminal unless the meter manufacturer specifies otherwise.
• Wait for the reading to stabilize. The multimeter charges the capacitor during measurement. Larger capacitors may take longer to produce a stable value. [3]
• Compare the reading with the rated value. Use the capacitor’s nominal capacitance and specified tolerance to determine whether the measured value is within its allowable range.
A capacitance reading within the specified tolerance indicates that the capacitor’s capacitance value is acceptable. However, this test alone cannot detect every fault, such as excessive ESR or leakage current. [1,6]
To interpret a capacitance measurement, compare the measured value with the capacitor's nominal capacitance and specified tolerance. Do not judge the result only by how close it appears to the value printed on the capacitor.
Calculate the minimum and maximum allowable capacitance using:
Minimum capacitance:
Cmin = CN (1 − T100 )
Maximum capacitance:
Cmax = CN (1 + T100 )
<p
where:
• Cn= nominal capacitance
• T= specified tolerance in percent
• Cmin= minimum allowable capacitance
• Cmax= maximum allowable capacitance
When a reading is close to a tolerance limit, consider the multimeter’s capacitance accuracy, resolution, measurement range, lead capacitance, temperature, and test method before rejecting the capacitor. Use the REL or zero function when measuring small capacitance values if the meter supports it.
Interpret the measurement using these limits:
• Within the allowable range: The measured capacitance is within specification.
• Below the minimum value: The capacitor has lower capacitance than specified and may be degraded or faulty.
• Above the maximum value: The capacitance is outside its specified tolerance and should be investigated further.
• No valid capacitance reading: Check the meter setting, test connections, and capacitor condition before drawing a conclusion.
Always use the tolerance specified on the capacitor or in its datasheet rather than an arbitrary percentage. A capacitance measurement evaluates the capacitance value only; Section 7 explains why a normal reading does not by itself confirm overall capacitor health. [1]
Resistance mode is only a screening test for a capacitor. It can provide a basic qualitative check when capacitance mode is unavailable, but it does not measure capacitance directly or determine whether the capacitor is within its specified capacitance tolerance.
Figure 3. Checking a Capacitor with a Digital Multimeter in Resistance Mode
After completing the safety steps in Section 1, follow these steps:
• Set the multimeter to resistance mode. Select a suitable resistance range or use auto-ranging if available.
• Connect the probes across the capacitor. For a polarized capacitor, observe the correct polarity according to the multimeter manufacturer’s instructions.
• Watch the resistance reading. The meter applies a small test voltage that begins charging the capacitor. On many digital multimeters, the reading may initially be relatively low and then rise toward a very high resistance or OL.
The observed behavior can provide useful clues:
• Resistance rises toward a high value or OL: This is consistent with capacitor charging and suggests that the capacitor is not obviously shorted.
• Persistently low resistance: A persistently low resistance reading may indicate a short circuit or severe leakage, but a standard resistance test cannot quantify leakage current. Confirm the result with the capacitor isolated and use an appropriate leakage-current tester when a conclusive measurement is required.
• The meter immediately displays OL: This does not necessarily mean the capacitor is open. Small capacitors may charge too quickly for the meter to show the resistance transition.
Resistance mode is mainly useful for screening for obvious shorts or abnormal charging behavior. It cannot accurately measure capacitance, ESR, or leakage current. Use capacitance mode or appropriate dedicated test equipment when a quantitative diagnosis is required.
A faulty capacitor is best identified by combining electrical measurements with physical inspection. One sign alone may not provide a definite diagnosis. [3]
Common signs include:
• Capacitance outside tolerance: The measured capacitance is below or above the manufacturer’s specified range.
• Possible short circuit: Resistance remains unusually low during testing.
• Possible open failure: The expected charging behavior is absent or abnormal.
• Bulging or swollen case: The capacitor body is visibly deformed.
• Venting or rupture: The pressure vent or case is damaged.
• Electrolyte leakage: Fluid, residue, or corrosion is visible around the capacitor.
• Damaged terminals or leads: Connections are loose, broken, burned, or corroded.
• Abnormal circuit behavior: Symptoms may include startup problems, excessive ripple, unstable voltage, overheating, or intermittent operation.
You can sometimes perform a basic check on a capacitor while it is still connected to the circuit, but in-circuit measurements are less reliable. Other components connected to the same nodes can affect what the multimeter sees. Parallel resistors can lower the measured resistance, other capacitors can add to the apparent capacitance, and semiconductor junctions or alternate current paths can change the charging behavior seen in resistance mode. [3,7]
For this reason, an in-circuit reading should be treated as a screening result rather than a final diagnosis. A reading that clearly indicates a short may still be useful, but an apparently normal or abnormal capacitance value can be misleading because the meter may be measuring more than the capacitor itself.
For a more accurate capacitance measurement, the capacitor should be electrically isolated from the surrounding circuit. In many cases, it is not necessary to remove the component completely. Lifting or disconnecting one lead is usually enough to break parallel circuit paths and allow the multimeter to measure the capacitor more directly. [3]
Out-of-circuit testing is therefore preferred when you need to compare the measured capacitance with the capacitor's rated value and tolerance. Always disconnect power and fully discharge the capacitor before lifting a lead or taking any measurement. [2,3]
Capacitor condition should be evaluated using the measured capacitance, specified tolerance, resistance-mode behavior, and physical condition together. The examples below show how common test results can be interpreted.
| Example | Rated Capacitance | Tolerance | Acceptable Range | Test Result | Resistance-Mode Behavior | Interpretation |
| Within specification | 100 µF | ±20% | 80–120 µF | 94 µF | Resistance rises toward a high value | Capacitance is within specification. Basic tests do not indicate an obvious fault. |
| Reduced capacitance | 100 µF | ±20% | 80–120 µF | 63 µF | Resistance may still rise normally | Capacitance is below the specified minimum and may indicate degradation. |
| Possible short circuit | 100 µF | ±20% | 80–120 µF | No meaningful capacitance reading | Resistance remains very low | Results are consistent with a possible internal short. |
| Possible open failure | — | — | — | No valid capacitance reading | May immediately show very high resistance or OL | OL alone does not prove an open capacitor. Confirm using other measurements and inspection. |
Note: Resistance-mode behavior alone should not be used to determine capacitor condition. For example, a capacitor with reduced capacitance may still appear to charge normally, while an immediate OL reading can also occur with a healthy small capacitor.
No. A normal capacitance reading shows only that the capacitor's measured capacitance is within its expected range under the multimeter's test conditions. [1,6]
A capacitor can still have faults that a basic capacitance measurement does not reveal, including:
• High equivalent series resistance (ESR)
• Excessive leakage current
• Abnormal behavior at its operating voltage
• Poor performance at the circuit's operating frequency
• Problems that appear only at elevated or low temperatures [4,6]
For example, an electrolytic capacitor may retain nearly its rated capacitance while its ESR has increased enough to cause excessive ripple, heating, or unstable circuit operation. [4]
If a capacitor measures within tolerance but the circuit still shows problems such as excessive ripple, overheating, or unstable voltage, additional testing may be required. Depending on the application, this can include ESR measurement, leakage-current testing, or impedance testing under appropriate operating conditions. [1,4,6]
A digital multimeter and an ESR meter measure different capacitor characteristics. A multimeter is mainly used to check capacitance against the specified value and tolerance, while an ESR meter measures the capacitor's equivalent series resistance. [3,7]
| Comparison | Digital Multimeter | ESR Meter |
| Main measurement | Capacitance value [3] | Equivalent series resistance (ESR) [7] |
| What it can detect | Capacitance outside tolerance and some obvious faults | Excessive internal resistance |
| Normal result | Capacitance is within specified tolerance | ESR is within the expected range for the capacitor type and rating |
| Main limitation | Does not normally measure ESR | Does not directly confirm capacitance is within tolerance |
| Useful for | General capacitance and tolerance checks | Troubleshooting electrolytic capacitors, especially in high-ripple circuits [4,7] |
| In-circuit testing | Often affected by surrounding components [3] | Some meters support in-circuit testing, although parallel paths can affect results [7] |
| Best approach | Use for capacitance measurement [3] | Use when ESR needs to be evaluated [7] |
The two instruments therefore provide complementary measurements. When a more complete capacitor evaluation is required, capacitance and ESR can be checked together. [6,7]
Technical References
[1] International Electrotechnical Commission. “Fixed Capacitors for Use in Electronic Equipment – Part 1: Generic Specification.” IEC, 2021. IEC 60384-1:2021, Edition 6.0.
[2] Keysight Technologies. “U1281A/U1282A Handheld Digital Multimeter Quick Start Guide.” Keysight Technologies, 2024. U1281-90000, Edition 4, May 2024.
[3] Fluke Corporation. “How to Measure Capacitance with a Digital Multimeter.” Fluke Corporation, n.d. Accessed September 24, 2026.
[4] Nichicon Corporation. “General Descriptions of Aluminum Electrolytic Capacitors.” Nichicon Corporation, n.d. Technical Notes CAT.8101E.
[5] Cornell Dubilier. “Aluminum Electrolytic Capacitor Application Guide.” Cornell Dubilier, n.d.
[6] HIOKI E.E. Corporation. “Electrolytic Capacitors.” HIOKI E.E. Corporation, n.d. Accessed September 24, 2026.
[7] Peak Electronic Design Limited. “Atlas ESR Gold: Equivalent Series Resistance Meter, Model ESR70, User Guide.” Peak Electronic Design Limited, 2021. EN70G-14, Rev. 14, November 2021
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