The Direct Answer: How to Measure Capacitance on a Multimeter

To measure capacitance on a multimeter, set the dial to the capacitor symbol (-|(-), insert the black lead into the COM jack and the red lead into the VΩ (or dedicated C) jack, completely discharge the capacitor, and place the probes across the terminals. A good reading falls within ±5% to ±10% of the component's rated microfarad (µF) or picofarad (pF) value. Anything outside this tolerance, or an "OL" (Over Limit) reading, indicates a failed component.

Modern digital multimeters (DMMs) like the Fluke 87V or Uni-Trend UT61E measure capacitance by either applying a constant current and measuring the voltage ramp rate (dV/dt) for larger electrolytic capacitors, or by injecting a high-frequency AC signal and calculating impedance for smaller ceramic capacitors. Because the meter must interact with the dielectric material to take a measurement, the component must be isolated from the circuit and fully discharged before testing.

Meter Setup Block:
  • Dial Position: Rotate to the capacitance symbol. On meters with a shared dial position (like Hz/Duty/Cap), you may need to press a yellow "Mode" or "Select" button to toggle into capacitance mode.
  • Lead Jacks: Black lead to COM. Red lead to VΩ (most modern meters) or the dedicated Cx jack (common on older or budget meters like the Mastech MS8268).
  • Range: Set to Auto-Range if available. If manual, start at the highest range (e.g., 100mF) and step down to prevent overloading the meter's internal ADC.

Safety First: Discharging and CAT Ratings for Capacitor Testing

Capacitors store lethal amounts of energy. A standard 45µF / 440VAC HVAC run capacitor holds enough charge to deliver a severe shock and will instantly blow the high-rupturing-capacity (HRC) fuse inside a $300 multimeter if probed while charged. According to Fluke's official testing guidelines, you must never assume a capacitor is dead just because the equipment is unplugged.

MANDATORY DISCHARGE PROCEDURE: Never short a large capacitor directly with a screwdriver. This causes a violent spark, damages the capacitor's internal metallization, and can weld the screwdriver to the terminals. Instead, use a 20kΩ, 5-watt wirewound resistor mounted on an insulated probe. Place the resistor across the terminals for 5 to 10 seconds, then verify with your DMM in DC Volts mode that the residual voltage reads 0.00V before switching to capacitance mode.

Safety Category (CAT) Requirements:
Your multimeter's CAT rating must match the environment where the capacitor lives. If you are testing a PCB in an isolated bench power supply, a CAT I meter is sufficient. If you are testing a motor run capacitor inside an HVAC condenser unit or a washing machine control board, you must use a CAT II or CAT III rated meter with appropriately rated test leads (typically 1000V CAT III). The CAT rating ensures the meter can safely handle transient voltage spikes on the mains line without internal arcing.

Probe Placement and Expected Readings: Good vs. Bad Capacitors

Probe placement depends on the capacitor chemistry. For non-polarized capacitors (ceramic, film, mica), probe orientation does not matter. For polarized electrolytic capacitors, the DMM outputs a very low test voltage (usually under 1V), meaning reverse polarity won't cause the capacitor to vent or explode during a brief bench test. However, best practice dictates placing the red probe on the anode (+) and the black probe on the cathode (-) to ensure the internal dielectric oxide layer is biased correctly during the charge cycle, yielding the most accurate reading.

Below is the expected reading table for common capacitor types. Note that electrolytic capacitors typically have a wider factory tolerance (±20%) compared to film capacitors (±5%).

Capacitor Type & Nominal Value Typical Application Good Reading (Pass) Bad Reading (Fail / Replace)
100nF (0.1µF) Ceramic IC Decoupling, PCB bypass 90nF – 110nF < 85nF, or "OL" (Open)
45µF / 440VAC Film HVAC Compressor Run Cap 42.7µF – 47.2µF (±5%) < 40.0µF, or > 50.0µF
1000µF / 35V Electrolytic Power Supply Filtering 800µF – 1200µF (±20%) < 800µF, or "0.00" (Short)
22pF Ceramic Microcontroller Crystal Oscillator 20pF – 24pF < 18pF, or > 30pF

When testing HVAC run capacitors, the ±5% tolerance is a hard industry standard. A 45µF capacitor reading 41µF might still "run" the compressor, but the shifted phase angle will cause the motor to draw excessive amperage, overheat, and fail prematurely. Always fail it at the 5% mark.

Five Mistakes That Give Misleading Capacitance Readings

If your readings are jumping around or seem physically impossible, you are likely falling victim to one of these common bench mistakes:

  1. Measuring In-Circuit: This is the most common error. Capacitors in parallel add together ($C_{total} = C_1 + C_2 + ...$). If you probe a 10µF capacitor while it's still soldered to a PCB, the meter will also read the parallel decoupling caps and the parasitic capacitance of the copper traces, giving you a wildly inflated reading. Always lift one leg of the capacitor or desolder it completely before testing.
  2. Finger Capacitance Interference: The human body has a parasitic capacitance of roughly 50pF to 100pF. If you are measuring small ceramic capacitors (e.g., 22pF) and you hold the bare metal probe tips with your fingers, your body will skew the reading. Use alligator clips or a dedicated SMD test tweezer for sub-nanofarad measurements.
  3. Residual Charge: If a capacitor is not fully discharged, the residual DC voltage will fight the DMM's internal test current. The meter's protection circuitry will either block the measurement (displaying "OL") or, in cheaper meters without robust input protection, blow the internal fuse.
  4. Ignoring Test Lead Capacitance: Standard 3-foot silicone test leads have an inherent parasitic capacitance of about 10pF to 15pF. When measuring very small values, you must use the meter's "Relative" (REL) or "Zero" mode. Short the probe tips together, press REL to subtract the lead capacitance, and then measure the component.
  5. Testing Swollen or Leaking Electrolytics: If an aluminum electrolytic capacitor has a domed vent, is leaking electrolyte, or smells like fish, do not test it. The capacitance value is irrelevant; the internal equivalent series resistance (ESR) has skyrocketed, and the part is dead. Discard and replace immediately.

For a deeper understanding of how dielectric absorption and ESR affect these measurements, refer to the All About Circuits textbook section on capacitor behavior, which explains why a standard DMM capacitance check doesn't always catch high-ESR failures in switching power supplies.

Decision Tree: Interpreting Your Reading and Next Steps

Use this decision path to determine your exact next step based on the DMM display. Do not guess; follow the logic to its concrete conclusion.

DMM Display / Symptom Diagnosis Concrete Action & Replacement Pick
Reading is within ±5% to ±10% of nominal Capacitor is healthy (assuming ESR is also acceptable for high-frequency circuits). Keep. Reinstall the component or re-solder the lifted leg.
Reading is 15% to 90% below nominal Dry electrolyte or degraded dielectric. The capacitor has lost its ability to store the rated charge. Replace. For a 1000µF 35V power supply cap, buy the Panasonic EEUFM1V102 (low ESR, 105°C rated). Match µF exactly; voltage rating can be equal or higher.
Reading is "OL", "1", or Out of Limits Open circuit. The internal foil has severed, often due to a voltage spike or thermal fatigue. Replace. For a 45µF HVAC run cap, install a TTC 45 MFD 440V Round Capacitor. Ensure the new physical dimensions fit the mounting strap.
Reading is "0.00", near zero, or meter beeps continuity Dead short. The dielectric layer has punctured, connecting the anode and cathode directly. Replace & Investigate. A shorted cap often means a downstream voltage regulator failed or a reverse-polarity event occurred. Replace with the exact OEM spec and check upstream diodes before applying power.
Reading fluctuates wildly (e.g., jumping from 10µF to 80µF) Intermittent internal connection or severe moisture ingress in the dielectric. Replace. Do not attempt to "dry out" or reflow the terminals. The internal structure is mechanically compromised.

Final Rule for Replacements: When sourcing a replacement, the microfarad (µF) rating must match the original exactly (especially for motor start/run circuits where phase shift is critical). The voltage rating (VDC or VAC) must be equal to or greater than the original. Never substitute a 25VDC capacitor for a 50VDC original, even if the capacitance value is identical; the thinner dielectric will fail under the higher voltage stress.