How To Read Aluminum Electrolytic Capacitors

4 min read Jun 26, 2024
How To Read Aluminum Electrolytic Capacitors

How to Read Aluminum Electrolytic Capacitors


Aluminum electrolytic capacitors are widely used in electronic circuits due to their high capacitance values and low cost. However, reading the markings on these capacitors can be challenging for many people. In this article, we will guide you on how to read aluminum electrolytic capacitors correctly.

Understanding the Markings

Aluminum electrolytic capacitors typically have several markings on their body, which provide essential information about the capacitor's characteristics. These markings include:

Capacitance Value

The capacitance value is usually expressed in microfarads (μF) and is printed on the capacitor body. You may see a notation like "10uF" or "100nF". The "u" or "n" denotes the unit of measurement, where "u" means microfarads and "n" means nanofarads.

Voltage Rating

The voltage rating is the maximum voltage that the capacitor can withstand. It is usually printed on the capacitor body in volts (V). For example, "50V" or "25V".


The tolerance indicates the allowed variation in the capacitance value. It is expressed as a percentage, such as "+/-10%" or "+/-20%".

Temperature Rating

The temperature rating specifies the operating temperature range of the capacitor. It is usually expressed in degrees Celsius (°C), such as "-40°C to +85°C" or "-25°C to +70°C".

ESR (Equivalent Series Resistance)

ESR is an important parameter that affects the capacitor's performance. It is usually printed on the capacitor body in ohms (Ω).


Some capacitors have a lifetime rating, which indicates the number of hours or years the capacitor is expected to last under specified conditions.

Example of a Capacitor Marking

Let's take an example of a capacitor marking:

220uF 50V 10% -40°C to +85°C

In this example:

  • Capacitance value: 220 microfarads (μF)
  • Voltage rating: 50 volts (V)
  • Tolerance: +/- 10%
  • Temperature rating: -40°C to +85°C

Tips and Precautions

  • Always handle capacitors with care to avoid damage or electrical shock.
  • Make sure to read the markings correctly to ensure the capacitor is suitable for your circuit.
  • Verify the capacitor's specifications with the manufacturer's datasheet to ensure accuracy.


Reading aluminum electrolytic capacitors may seem daunting at first, but with practice and understanding of the markings, you can easily identify the capacitor's characteristics. Remember to always follow proper safety precautions when handling capacitors and consult the manufacturer's datasheet for accurate specifications.