The Direct Answer: How to Check Capacitance with a Multimeter

To check capacitance with a digital multimeter (DMM), set the dial to the capacitance symbol (⊣⊢), insert the black lead into the COM jack and the red lead into the VΩ jack. Completely discharge the capacitor, remove it from the circuit, and touch the probes to the component leads. A good reading falls within ±20% of the rated microfarad (µF) value printed on the capacitor jacket for standard electrolytics, or ±5% for precision film capacitors. If the meter reads "OL" (open) or a value significantly below the tolerance band, the capacitor has failed and must be replaced.

Meter Setup and Safety Category Requirements

Before touching any probes, you must configure your meter correctly and verify its safety rating for the environment you are working in. Capacitors in mains-powered equipment (like HVAC run capacitors or ATX power supplies) can store lethal energy and deliver catastrophic arc flashes if a meter fails internally during a test.

SAFETY CATEGORY (CAT) REQUIREMENT: Never use a CAT I or CAT II rated meter to test capacitors connected to mains voltage circuits (e.g., 120V/240V AC lines). You must use a CAT III 600V or CAT IV 600V rated multimeter and matched test leads. Meters like the Fluke 117 or Klein Tools MM400 meet these requirements. The internal blast shields and high-energy fuses in CAT III/IV meters prevent arc-over if a charged capacitor shorts through the meter's test circuitry.

Meter Setup Block

  • Dial Position: Rotate the selector to the capacitance function. On most meters, this is a dedicated setting marked with the capacitor symbol (two parallel lines, one curved or both straight). On some auto-ranging meters, it shares a position with the Ohms (Ω) or continuity setting and requires pressing a secondary "Hz/CAP" toggle button.
  • Lead Jacks: Black lead to COM (Common). Red lead to VΩ (Volts/Ohms). Never use the high-current (A or mA) jacks for capacitance testing; the internal shunt resistors will short the capacitor and blow the meter's fuse.
  • Range Setting: If your meter is manual-ranging, start at the highest µF range (e.g., 2000µF or 20mF) and step down until you get a stable reading without the "OL" (Over Limit) indicator. Auto-ranging meters will handle this sweep automatically, though it may take 3 to 5 seconds to lock onto large values.

Step-by-Step Probe Placement and Discharge Protocol

A standard DMM measures capacitance by applying a low-voltage AC test signal and calculating the reactance. While this test signal is non-polarized, proper bench discipline requires a strict discharge and isolation sequence.

  1. De-energize and Isolate: Turn off the equipment, unplug it, and switch off the relevant breaker. For HVAC systems, pull the disconnect block. Verify the circuit is dead using the AC voltage function on your CAT-rated meter.
  2. Discharge the Capacitor: Never short a capacitor with a screwdriver; this damages the internal metallization and can weld the tool to the terminals. Use a 20kΩ, 5-watt bleeder resistor attached to insulated alligator clips. Bridge the resistor across the capacitor terminals for 10 to 15 seconds. Verify the voltage is below 1V DC with your multimeter before proceeding.
  3. Isolate from the Circuit: Desolder or physically disconnect at least one leg of the capacitor from the PCB or terminal block. Testing in-circuit will yield wildly inaccurate readings due to parallel impedance paths.
  4. Zero the Leads (Relative Mode): Touch the probe tips together. The meter will read the parasitic capacitance of the test leads (usually 0.05nF to 0.2nF). Press the "REL" (Relative) or "ZERO" button to subtract this baseline. This is critical when measuring small ceramic or film capacitors under 1nF.
  5. Probe Placement: Touch the red probe to the anode (+) and the black probe to the cathode (-) of electrolytic capacitors. For non-polarized film or ceramic capacitors, probe orientation does not matter. Hold the probes firmly to the metal leads, not the plastic jacket, and wait for the reading to stabilize.

Expected Reading Table: Good vs. Bad Capacitor Values

Capacitors degrade over time as their internal electrolyte dries out or their dielectric layer breaks down. According to Fluke's electrical testing guidelines, a capacitor is considered out-of-spec if it drifts beyond its manufacturer-stated tolerance. Standard aluminum electrolytics typically carry a ±20% tolerance (M-code), while precision film caps are usually ±5% (J-code) or ±10% (K-code).

Rated Value (Printed) Type & Tolerance Good Reading Range (Pass) Bad Reading: Drifted / Dried Out Bad Reading: Short / Open
0.1µF (104) Ceramic (±10%) 0.090µF to 0.110µF < 0.085µF 0.000µF or OL
10µF Film (±5%) 9.50µF to 10.50µF < 9.00µF or > 11.00µF OL (Open Internal Lead)
470µF Electrolytic (±20%) 376µF to 564µF < 350µF (Severe Dry-out) 0.00µF (Shorted Dielectric)
1000µF Electrolytic (±20%) 800µF to 1200µF < 750µF (High Ripple Risk) OL or 0.00µF
45µF (HVAC Run) Metallized Film (±6%) 42.3µF to 47.7µF < 40.0µF (Motor Won't Start) OL (Blown Internal Fuse)

Common Mistakes That Give Misleading Readings

If your measurements seem erratic or contradict the physical state of the circuit, you are likely falling victim to one of these bench errors. For a deeper look into component behavior, SparkFun's capacitor tutorial covers the underlying physics of dielectric absorption and parasitic effects.

1. The In-Circuit Parallel Trap: Measuring a capacitor while it is still soldered to a PCB will almost always yield a reading higher than the rated value. The multimeter's test signal travels through parallel copper traces, inductors, and semiconductor junctions, summing the parasitic capacitance of the entire board. Always lift one leg.

2. Ignoring Dielectric Absorption (Voltage Rebound): If you discharge a large electrolytic capacitor, remove the bleeder resistor, and wait five minutes, the capacitor will spontaneously regenerate a voltage (sometimes 10V to 20V) due to dielectric absorption. If you apply multimeter probes during this rebound, the back-EMF can confuse the DMM's analog-to-digital converter, resulting in a wildly fluctuating or negative capacitance reading. Always discharge immediately before probing.

3. The ESR Blind Spot: This is the most dangerous mistake in modern electronics repair. A standard multimeter measures capacitance (the ability to store charge), but it cannot measure Equivalent Series Resistance (ESR). A 1000µF filter capacitor in a switching power supply might read a perfect 980µF on your DMM, but if its internal ESR has spiked from 0.05Ω to 2.0Ω due to electrolyte degradation, it will fail to filter high-frequency ripple, causing the power supply to overheat and shut down. A DMM will tell you if a capacitor is open or shorted, but it will not tell you if it is "weak" under load.

Decision Path: Replace, Retest, or Upgrade Your Tool

Use this decision tree to determine your next action based on your multimeter's reading and the circuit's behavior. Do not rely on guesswork when dealing with power delivery networks.

Condition / Symptom Multimeter Reading Required Action
Circuit works fine; performing routine preventative bench check. Within ±20% of rated µF. KEEP. Reinstall the component. No further action required.
Circuit is dead; capacitor shows physical bulging or vented electrolyte. Any reading (even if within spec). REPLACE. Physical deformation indicates internal gas buildup. Replace with identical µF, but upgrade the voltage rating (e.g., swap a 16V cap for a 25V or 50V cap) for longer life.
Circuit is dead; reading is >20% below rated µF. Low µF value (e.g., 470µF reads 210µF). REPLACE. The electrolyte has boiled off. The component is electrically exhausted.
Meter reads "OL" or 0.00µF consistently. Open or Shorted. REPLACE. Internal lead wire has snapped (OL) or dielectric has punctured (0.00µF).
Switching power supply fails under load, but capacitor reads perfect µF on DMM. Within ±20% of rated µF. UPGRADE TOOL. Your DMM cannot see the high ESR causing the failure. You must test with a dedicated ESR meter.

The Concrete Recommendation for ESR Testing

If your decision path terminates at the final row—where capacitance reads fine but the circuit still fails due to suspected high ESR—you must stop using a standard DMM for this diagnostic. The default, industry-standard tool for this specific job is the Peak Atlas ESR70 (or the newer ESR70+ variant). Unlike a standard multimeter, the ESR70 injects a 100kHz AC test signal that bypasses the capacitive reactance and measures only the resistive losses of the internal electrolyte, allowing you to test capacitors in-circuit without desoldering them. If you are repairing motherboards, LCD inverters, or ATX power supplies, adding an ESR meter to your bench is not optional; it is the only way to definitively clear a capacitor as "good."