Master the Basics: How to Read Capacitor Values

Understanding capacitor values is crucial when working with electronic circuits. While some capacitors have values clearly printed on them, others use a coded numbering system. This guide will teach you how to read capacitor values and measure capacitance using a digital multimeter.

Reading Electrolytic Capacitor Values

Electrolytic capacitors, which are cylindrical and resemble small tin cans, have their capacitance value and maximum voltage rating printed directly on the side. These values are usually easy to read.

• The capacitance is measured in microfarads (µF).
• The maximum voltage rating indicates the highest voltage the capacitor can handle.
• Electrolytic capacitors are polarized, meaning they have a positive and negative terminal. The negative side is marked with a minus (-) symbol.

Example: A capacitor labeled 1000µF 25V has a capacitance of 1000 microfarads and can withstand up to 25 volts.

Reading Ceramic Capacitor Values

Ceramic capacitors are much smaller and often use a numerical code instead of direct labeling. The most common coding system uses three digits to express capacitance in picofarads (pF).

• The first two digits represent significant figures.
• The third digit indicates the multiplier (as a power of 10).

Example:

• A capacitor labeled 103 means: 10 × 10³ = 10,000 picofarads (or 10 nanofarads).
• A capacitor labeled 334 means: 33 × 10⁴ = 330,000 picofarads (or 330 nanofarads).

Understanding Capacitor Tolerance Codes

Capacitors have a tolerance rating that indicates how much their actual capacitance may vary from the stated value. This is often represented by a letter following the three-digit code.

Common Tolerance Letters:

• B, C, D: Represent tolerance in picofarads (±10pF, ±20pF, etc.).
• F through Z: Represent tolerance as a percentage of the nominal value.
• K: ±10%
• M: ±20%
• Z: Wide tolerance range (from +80% to -20%).

Example: A capacitor labeled 334K has a capacitance of 330 nanofarads with a ±10% tolerance, meaning its actual value could be between 297 and 363 nanofarads.

Using a Digital Multimeter to Measure Capacitance

Not all digital multimeters (DMMs) have a capacitance measurement feature. If your DMM supports it, follow these steps:

1. Turn the knob to the capacitance measurement mode (often marked with a capacitor symbol).
2. Connect the multimeter probes to the capacitor terminals.
3. The display will show the measured capacitance, which should be within the expected tolerance range.

For accurate readings, ensure the capacitor is discharged before measuring.

Takeways

Understanding how to read capacitor values is a vital skill for electronics beginners. While electrolytic capacitors display their values directly, ceramic capacitors require decoding their three-digit marking system. By learning to interpret these values and using a multimeter, such as Fluke 101 Digital Multimeter when needed, you can confidently select the right capacitors for your electronic projects.