You can measure a capacitor’s value using a digital multimeter with a capacitance mode, which is the most common and accessible method. The process involves discharging the capacitor, removing it from the circuit, setting your meter to the capacitance setting (marked with a “C” or the Farad symbol), and touching the leads to the terminals. The reading tells you the capacitance in microfarads (µF), nanofarads (nF), or picofarads (pF). But getting an accurate, meaningful result takes a bit more care than just touching probes to legs.
Discharge the Capacitor First
Capacitors store electrical energy, and they can hold a charge long after the power is turned off. Before you measure or even touch a capacitor, you need to discharge it safely. Start by turning off and unplugging the device. Then use a multimeter set to voltage mode to confirm there’s no charge remaining.
If the capacitor still shows voltage, discharge it by connecting a resistor across both terminals. A 20,000-ohm, 5-watt resistor is a standard choice for this. Hold it across the leads for about five seconds, then re-check with your multimeter. If voltage remains, repeat until the reading hits zero. For low-voltage capacitors (under 50 volts), you can bridge both terminals with an insulated screwdriver, but for anything higher, the resistor method is safer and more controlled.
Wear insulated gloves and safety glasses whenever you’re working with capacitors, especially large ones from power supplies, microwave ovens, or motor circuits. These can carry enough energy to cause serious injury.
Remove the Capacitor From the Circuit
For an accurate reading, desolder or disconnect the capacitor from the circuit board before measuring. When a capacitor is still connected in-circuit, other components create parallel paths that distort your reading. Resistors, inductors, and neighboring capacitors all contribute their own electrical characteristics, and your multimeter can’t distinguish the capacitor’s value from the combined effect of everything around it. Fluke, one of the most widely used multimeter manufacturers, specifically recommends detaching the capacitor to avoid measurement errors.
If desoldering isn’t practical, at minimum disconnect one leg of the capacitor from the board. This breaks the parallel path and gives your meter a much better shot at an accurate reading.
How to Read Capacitor Markings
Before measuring, it helps to know what value you’re expecting. Electrolytic capacitors usually print their value directly on the body, something like “470µF 25V.” Ceramic capacitors use a three-digit code that trips people up.
The code works like this: the first two digits are a base value in picofarads, and the third digit is a multiplier (the number of zeros to add). A capacitor stamped “104” means 10 followed by four zeros, giving you 100,000 pF, which equals 100 nF or 0.1 µF. A code of “152” means 15 with two zeros added: 1,500 pF. If the code is only one or two digits, like “47,” that’s simply 47 pF with no multiplier.
Here are the most common codes you’ll encounter:
- 101: 100 pF (0.1 nF)
- 102: 1,000 pF (1 nF)
- 103: 10,000 pF (10 nF)
- 104: 100,000 pF (100 nF or 0.1 µF)
- 105: 1,000,000 pF (1 µF)
Measuring With a Digital Multimeter
Most modern digital multimeters include a capacitance mode, though budget models sometimes skip it. Look for a symbol on the dial that resembles two parallel lines or the letters “F” or “C.” On many meters, capacitance shares a dial position with another function, so you may need to press a secondary button to activate it. Check your meter’s manual if it’s not obvious.
Once you’ve discharged the capacitor and removed it from the circuit, turn the dial to capacitance mode and connect the test leads to the capacitor’s terminals. Give the meter a few seconds to auto-range and settle on a reading. The display will show the measured capacitance along with the unit.
For polarized capacitors like electrolytics, connect the red (positive) lead to the positive terminal and the black lead to the negative terminal. You can identify the positive terminal by the longer lead on a new capacitor, and the negative terminal by the stripe or band printed on the body, often marked with minus signs. Ceramic and film capacitors are non-polarized, so lead orientation doesn’t matter.
What Counts as a Good Reading
Capacitors are not precision components. A reading that seems “off” from the labeled value might be perfectly normal. Standard aluminum electrolytic capacitors commonly have a tolerance of plus or minus 20%, meaning a 100 µF capacitor reading anywhere from 80 µF to 120 µF is within spec. Some electrolytics allow even wider swings, up to +80% on the high side. Film capacitors tend to be tighter, around 5% to 10%, and high-precision types used in audio equipment can be rated at 1% or less.
If your capacitor reads significantly outside its tolerance range, particularly if it reads very low, that’s a strong sign of failure. A 100 µF electrolytic reading 30 µF has lost most of its ability to store charge and should be replaced.
Why a Multimeter Might Not Be Enough
A digital multimeter answers one question: is the capacitance value roughly correct? It does this by charging the capacitor with a small current and timing how long it takes to reach a set voltage. This method is simple and fine for basic troubleshooting, but it can’t detect a capacitor that reads the right value yet performs poorly in a real circuit.
The missing piece is ESR, or equivalent series resistance, which is the internal resistance of the capacitor. As electrolytic capacitors age, their ESR rises even while their capacitance value stays close to normal. High ESR causes voltage ripple, heat, and instability in power supplies and other circuits. A healthy electrolytic in the 1 to 10 µF range at 400V typically has an ESR of 3 to 5 ohms. Lower-voltage, higher-capacitance parts should measure well under 1 ohm. A failed capacitor often shows ESR values an order of magnitude higher than expected.
To measure ESR, you need either a dedicated ESR meter or an LCR meter. An LCR meter applies a pure sine wave at a controlled frequency and measures the phase relationship between voltage and current. This lets it separate the capacitance from the resistance and loss characteristics. Where a multimeter has an accuracy of roughly 1% to 10%, an LCR meter can achieve 0.05% or better, and it can test at the actual frequency the capacitor operates at in your circuit. For repair work on power supplies, amplifiers, or motherboards where bad capacitors are a common failure mode, an ESR meter is one of the most useful tools you can own.
Choosing the Right Tool for the Job
For most hobbyists and DIY repair work, a digital multimeter with a capacitance mode handles the vast majority of situations. If you’re checking whether a capacitor is dead, shorted, or wildly out of spec, it gives you a fast, clear answer. These are also the most affordable option, since many general-purpose multimeters already include the function.
If you’re diagnosing intermittent problems in electronics, especially swollen or suspect electrolytic capacitors on circuit boards, a dedicated ESR meter pays for itself quickly. These typically cost between $20 and $80 and can test capacitors in-circuit with reasonable accuracy, since they use a high-frequency, low-voltage signal that doesn’t activate surrounding components the way a standard capacitance test does.
LCR meters sit at the professional end. They’re the right tool when you need to characterize a capacitor’s full behavior across frequencies, verify incoming parts for quality, or do design work where the loss factor and quality factor matter. Benchtop models start around $200 and go up from there, with handheld versions available for less. Unless you’re doing engineering-level work, a multimeter combined with an ESR meter covers nearly every practical scenario.