A digital multimeter can test a capacitor by measuring its capacitance, and a reading far off the marked value means the part is likely bad.
A swollen capacitor — or a board that suddenly quit — is one of the most frustrating electronics failures. The good news: you can figure out how to test a capacitor with a multimeter in about a minute, and the procedure tells you plainly whether the part is good or garbage.
A digital multimeter’s capacitance mode measures the part in microfarads (µF) and compares it against the value printed on the capacitor’s body. This guide covers the discharge step, the correct dial settings and lead connections, and how to read the result — including the OL warning that confuses most beginners.
Why Test a Capacitor With a Multimeter?
A capacitance reading identifies a bad part in seconds without guesswork. A capacitor that has drifted out of spec drags down everything around it, so testing directly beats replacing parts on a hunch.
Capacitors store charge, smooth power delivery, and help motors start. When one fails, symptoms range from a flickering light to a device that refuses to power on — so a quick multimeter test pinpoints the culprit before you spend money on replacement parts.
Testing a Capacitor: The Step Order That Works
The complete sequence is: kill power, discharge the capacitor, remove it from the circuit, set the meter to capacitance mode, connect the leads, and compare the reading with the rated value.
- Turn the power off and confirm it’s dead. Unplug the device or flip the breaker, then verify zero volts at the capacitor terminals using the meter’s AC or DC voltage setting.
- Discharge the capacitor. Hold a 20,000 Ω, 5-watt resistor across the terminals for five seconds to drain the stored charge — shorting the leads with a screwdriver can damage the part and the meter.
- Pull the capacitor out of the circuit. In-circuit measurements pick up parallel components and read wrong, so desolder or unclip at least one lead; removing the whole part is cleaner.
- Set the dial to capacitance mode. Look for the –||– symbol or the µF mark. On many meters this position is shared with another function, so press the function button until capacitance mode is active; exact button names vary by model.
- Connect the leads. Black goes to COM, red goes to the capacitance jack, and the probes touch the two capacitor terminals. For polarized capacitors, keep the red probe on the positive terminal.
- Wait a few seconds for the meter to auto-range, then note the value. The display settles on a fixed number — that’s your reading.
One refinement: when you measure low-value capacitors, the test leads themselves add a few picofarads of capacitance. Switch on Relative mode (REL) to zero out the leads before touching the part.
If you test capacitors regularly, a dedicated capacitance tester reads parts in seconds and handles checks a multimeter can’t. Our tested picks for the best capacitor testers cover the models worth owning.
What the Reading Tells You
A healthy capacitor reads within 10–20% of its printed value, depending on type. A reading far outside that band — or an OL on the display — means the part is suspect.
Compare the measured microfarads to the number stamped on the capacitor and apply the tolerance. A 47 µF electrolytic that reads 30 µF has lost a third of its capacitance and should be replaced. If the meter shows OL, the part either exceeds the range or has failed open; Fluke’s guide to measuring capacitance explains the overrange display in detail.
What Does OL Mean?
OL stands for overrange. It appears when capacitance exceeds the meter’s current range, so switch to the next higher range first. If OL persists on the highest range, the capacitor is almost certainly open or faulty.
The two classic errors are measuring while the part is still in the circuit and skipping the discharge step. Both produce misleading readings or a shock hazard. When in doubt, pull the capacitor, discharge it, and start over.
| Meter Reading | What It Means | Verdict |
|---|---|---|
| Within 10–20% of rated value | Capacitance is healthy | Keep the part |
| Well below rated value | Capacitance has degraded | Replace it |
| OL on every range | Open internal connection | Replace it |
| Near zero | Short between the plates | Replace it |
FAQs
Can You Test a Capacitor Without Removing It From the Circuit?
You can get a rough idea, but in-circuit readings are usually inaccurate because parallel components affect the measurement. Remove at least one lead from the circuit before trusting the result. A dedicated capacitor tester with an in-circuit mode is the exception, since it works differently from a multimeter’s capacitance setting.
What Does OL Mean When Testing a Capacitor With a Multimeter?
OL stands for overrange, meaning the capacitance reading exceeds the meter’s selected range. Switch to a higher range if your meter offers one. If OL still appears on the highest range, the capacitor is very likely open or otherwise faulty and should be replaced.
Do You Need to Discharge a Capacitor Before Testing It?
Yes, always. A charged capacitor can deliver a painful shock and can damage the meter’s input circuitry. Place a 20,000 Ω, 5-watt resistor across the two terminals for five seconds, then confirm with the multimeter that the voltage reads zero before you touch the part.
References & Sources
- Fluke Corporation. “How to Measure Capacitance.” Fluke’s guide to measuring capacitance with a digital multimeter, covering lead placement, range limits, and the OL overrange display.