Capacitor Calculator

Understanding Capacitor Codes

A capacitor stores electrical energy in an electric field and is one of the most common components in every electronic circuit, from the decoupling capacitors beside every integrated circuit to the filter capacitors in a power supply. The trouble for anyone reading a schematic or repairing a board is that a capacitor's physical size gives no clue to its value, and the markings on the component itself use a compact code that is opaque until you know the system. A capacitor calculator decodes those markings, reverses the process when you need to order a part, and computes the reactance that governs how a capacitor behaves in an alternating-current circuit. [wiki-capacitor]

The international standard that governs these markings is IEC 60062, maintained by the International Electrotechnical Commission. It defines the numeric code systems, the tolerance letters, and the preferred value series that manufacturers print on capacitors and resistors. Understanding this standard turns an apparently random string like "104" into an unambiguous capacitance value in seconds. [iec60062]

There are three distinct operations this calculator handles, because they arise at different moments in a project. When you find a component on a board or in a parts bin, you decode its printed code to learn its value. When you design a circuit and need to order a capacitor, you encode a desired value into the standard marking. When you analyze how the capacitor behaves in an AC circuit, you compute its capacitive reactance. The three modes of this calculator mirror those three needs. [electronics-notes]

Capacitance is measured in farads, but a one-farad capacitor is an enormous device. Practical capacitors are measured in microfarads (µF, one millionth of a farad), nanofarads (nF, one thousandth of a microfarad), and picofarads (pF, one trillionth of a farad). The relationship between the units is powers of ten: 1 µF = 1,000 nF = 1,000,000 pF. The EIA codes on small capacitors are always expressed in picofarads, no matter the final value, which is why understanding the unit conversion is the first step in reading them. [wiki-capacitance]

If you work with both capacitors and resistors, the Resistor Calculator handles the companion color codes and value conversion, while the Ohm's Law Calculator computes the current and power relationships in the circuits where both components appear. For sizing the copper in the power-delivery traces that feed those circuits, the Voltage Drop Calculator is a useful companion, and the Electricity Calculator covers the energy and cost side of a power supply design.

How to Use This Calculator

This calculator has three modes, selected from the dropdown at the top. Each mode computes its results automatically as you type.

The Capacitor Equations

Two relationships drive every result on this page: the code conversion and the reactance formula.

Common EIA Codes Reference

These are the capacitor codes you will encounter most often in practice, spanning four orders of magnitude. The table shows the code, its picofarad value, the nanofarad and microfarad equivalents, and the typical use.

The E-series preferred values are visible in the table: the significant figures 10, 22, 47, and 68 repeat because they belong to the logarithmic E12 series. Manufacturers produce capacitors at these preferred values, not at arbitrary numbers, so a design that specifies a standard value like 47 nF is far easier to source than one that demands a non-standard 53 nF. [iec60062]

Practical Tips for Reading Capacitors

Always identify the capacitor type before decoding. Ceramic disc capacitors use picofarad-based 3-digit codes; electrolytic capacitors almost always print the full value in microfarads plus the working voltage, such as "47 µF 25 V," and do not use the code system at all. Applying the code decoder to an electrolytic capacitor is a common and expensive mistake. [electronics-notes]

Watch for the letter R, which is not a tolerance code but a decimal point in low-value markings. A capacitor marked 4R7 is 4.7 pF, and one marked 0R5 is 0.5 pF. Values below 10 pF are too small for the standard two-figure-plus-multiplier code, so manufacturers fall back to this R-notation instead. [circuitdigest]

Read the tolerance before you trust the value in a timing circuit. A timing capacitor with a 20 percent tolerance will shift the timing of a 555 timer circuit by the same 20 percent, which can be the difference between a working circuit and a malfunctioning one. For precision timing, specify a 1 or 5 percent film or silver-mica capacitor and a code with a J or F tolerance letter. [book-art-electronics]

Remember that the code is not a guarantee of the exact value. Ceramic capacitors, especially those with Class 2 dielectrics like X7R and Y5V, can shift their capacitance dramatically with applied voltage and temperature, sometimes by 20 to 80 percent. A nominal 100 nF X7R capacitor may measure 50 nF at its rated DC bias. If the exact value matters, verify it with a multimeter in capacitance mode. [passive-components]

For power-supply and audio applications, mind the working voltage as well as the capacitance. The code typically omits the voltage rating entirely on small capacitors, and it is a separate line on electrolytics. A capacitor used near its voltage limit fails prematurely and, for electrolytic types, can vent or burst. Always derate to at least 80 percent of the rated voltage in practice.

When ordering replacement parts, note whether the capacitor is polar or non-polar. Electrolytic and tantalum capacitors are polarized and must be installed in the correct orientation; reversing them destroys the part and can damage the circuit. Ceramic and most film capacitors are non-polar and can be installed either way, which is one reason they dominate high-frequency applications.

Limitations

The code decoder assumes a standard IEC 60062 numeric marking. Some manufacturers, particularly for SMD components, print incomplete codes or use proprietary markings, and very small SMD capacitors may carry only a single character or no marking at all. When a code does not fit the 3 or 4 digit pattern, the calculator reports an error and the value must be confirmed by measurement. [iec60062]

The tolerance letter applies to the nominal value, not to a hard guarantee across temperature and voltage. Real capacitors drift with operating conditions, and the printed tolerance is a room-temperature, low-voltage figure. For precision applications, the only reliable numbers come from a calibrated capacitance meter.

The reactance calculation models an ideal capacitor. Real capacitors have equivalent series resistance (ESR), equivalent series inductance (ESL), and dielectric losses that grow in importance at high frequency. Above the capacitor's self-resonant frequency, the component behaves as an inductor rather than a capacitor, and the ideal reactance formula diverges sharply from reality. [wiki-capacitor]

The value-to-code encoder rounds to two significant figures, the maximum precision of a 3-digit code. If your design requires tighter precision than 2 percent, the encoder's rounded code is only an approximation and you should select a capacitor from the appropriate E-series with the needed tolerance. The 4-digit code provides three significant figures and is used for the largest values.

Finally, the calculator does not account for the dielectric type, temperature coefficient, or voltage rating, all of which are essential when selecting a part for a specific application. The capacitance value is only one of the specifications a real capacitor must meet.

Frequently Asked Questions

❓ How do I read a 104 capacitor code?

✅ The 104 code means 10 followed by 10 to the fourth power, which is 100,000 picofarads. That equals 100 nanofarads or 0.1 microfarads. The first two digits are the significant figures and the third is the number of zeros to add, always in picofarads.

❓ What does the K in 104K mean?

✅ The K is a tolerance letter meaning plus or minus 10 percent. A 104K capacitor is 100 nF with an actual value between 90 and 110 nF. J means 5 percent, M means 20 percent, and F means 1 percent.

❓ What is the difference between 3-digit and 4-digit codes?

✅ A 3-digit code uses two significant figures plus a multiplier and covers values below about 100 µF. A 4-digit code uses three significant figures plus a multiplier and is reserved for values of 1 µF and above, where the extra digit provides needed precision.

❓ What is capacitive reactance?

✅ Capacitive reactance is the opposition a capacitor presents to alternating current, measured in ohms. It equals 1 divided by 2 pi times the frequency times the capacitance. Reactance falls as frequency or capacitance rises, so a capacitor passes high frequencies easily and blocks low ones.

❓ How do I convert microfarads to picofarads?

✅ Multiply microfarads by one million to get picofarads, or by one thousand to get nanofarads. A 0.1 µF capacitor is 100 nF and 100,000 pF. The EIA code system always works in picofarads.

❓ Do electrolytic capacitors use these codes?

✅ Usually not. Electrolytic capacitors print their value and working voltage directly, such as 47 µF 25 V, because they are large enough to fit the text. The numeric code system is used on small ceramic, film, and tantalum capacitors where space is limited.

❓ What does the letter R mean on a capacitor?

✅ R is a decimal point in low-value markings. A capacitor marked 4R7 is 4.7 pF, and 0R5 is 0.5 pF. It appears only for values below 10 pF where the standard two-figure code cannot represent the value.

❓ How does capacitor size relate to value?

✅ It does not directly. A physically large capacitor can have a small capacitance if it uses a low-permittivity dielectric and a small electrode area, while a tiny multilayer ceramic can store a relatively large charge. The printed code is the only reliable indicator of value.

❓ What happens if I use a capacitor with too low a voltage rating?

✅ The capacitor may fail catastrophically, and electrolytic types can vent or burst. Always choose a capacitor whose voltage rating exceeds the maximum voltage in the circuit, with a typical derating margin of 20 percent or more.

❓ Why does capacitance drift with temperature?

✅ Class 2 ceramic dielectrics like X7R and Y5V have high permittivity that varies with temperature and applied voltage, shifting capacitance by 20 to 80 percent. Class 1 dielectrics like C0G and NP0 are stable but have much lower capacitance density, so they are used where stability matters more than value.