Capacitor Code Calculator Guide: Read 3-Digit Codes

Small ceramic capacitors rarely have room for their value printed in full. Instead, they carry a three-digit code stamped on a body a few millimetres across, and reading that code is a basic skill for anyone repairing electronics, building circuits, or sorting a parts box. The code is compact and logical once you know the rule, but it is also easy to misread, especially when the third digit is zero or when the units change between picofarads, nanofarads, and microfarads.

The Capacitor Code Calculator takes a 3-digit code and returns its value in picofarads, nanofarads, and microfarads, with the decoding shown step by step. This guide explains the rule, works through examples, and covers what the code does not tell you, which matters as much as what it does.

The decoding rule

The rule mirrors the resistor colour-code idea, but with digits. The first two digits are the significant figures, and the third digit is the multiplier: the number of zeros to add after those figures. The result is in picofarads. So a code of 104 means the figures 10, followed by 4 zeros, giving 100,000 picofarads. A code of 223 means 22 followed by 3 zeros, giving 22,000 picofarads. A code of 470 means 47 followed by 0 zeros, giving 47 picofarads.

Converting picofarads to larger units is a matter of dividing by 1,000 at each step: 1,000 picofarads equal 1 nanofarad, and 1,000 nanofarads equal 1 microfarad. So 100,000 picofarads equal 100 nanofarads, which equal 0.1 microfarads. Keeping the three units side by side prevents the most common error, which is quoting a value in the wrong unit and being out by a factor of a thousand.

Worked example: code 104, step by step

Take the code 104. Step one, split the digits: first digit 1, second digit 0, third digit 4. Step two, the significant figures are the first two digits together, which is 10. Step three, the multiplier is the third digit, 4, meaning add 4 zeros after 10. Step four, write it out: 10 followed by four zeros is 100,000. So the value is 100,000 picofarads.

Step five, convert: 100,000 picofarads divided by 1,000 equals 100 nanofarads, and 100 nanofarads divided by 1,000 equals 0.1 microfarads. So code 104 means 100,000 picofarads, 100 nanofarads, or 0.1 microfarads, all the same value in different units. This is one of the most common ceramic capacitor values, used for decoupling and filtering in countless circuits, which is why it makes a good example to memorise.

Try a second code to confirm the pattern. Code 223: significant figures 22, multiplier 3 zeros, giving 22,000 picofarads, which is 22 nanofarads, or 0.022 microfarads. Code 471: figures 47, multiplier 1 zero, giving 470 picofarads, which is 0.47 nanofarads. And code 100: figures 10, multiplier 0 zeros, giving 10 picofarads exactly, a useful reminder that a third digit of zero means no zeros are added, not that the value is zero.

What the code does not tell you

The three-digit code gives capacitance only. It says nothing about voltage rating, tolerance, temperature behaviour, or dielectric type, all of which matter when choosing a replacement. A capacitor rated for 50 volts cannot safely replace one rated for 100 volts in a high-voltage circuit, even if the capacitance matches, and a capacitor with a wide tolerance may behave differently from a tight-tolerance part in a timing or tuning circuit.

Additional markings sometimes carry that information: a letter after the code often indicates tolerance, and the capacitor's size, colour, and type hint at its voltage rating and dielectric, but those markings vary by manufacturer and era. When replacing a capacitor, match capacitance, match or exceed voltage rating, match the dielectric type where it matters, and check tolerance for sensitive circuits. The code alone is never the full specification.

Common mistakes

The most common mistake is treating the third digit as part of the value rather than as a zero count, so 104 is misread as 104 picofarads instead of 100,000. The second mistake is a unit error: quoting 100,000 picofarads as 100 microfarads instead of 0.1 microfarads, an error of a thousand times. Always convert step by step, dividing by 1,000 at each unit change, and sanity-check against common values: most small ceramic capacitors fall between a few picofarads and a few microfarads.

The third mistake is reading the code upside down or confusing it with a date or batch code printed nearby. Capacitor bodies can carry several markings, and the capacitance code is usually the most prominent three digits, but a second set of characters may be a tolerance letter or a manufacturer code. If a reading gives a bizarre value, check the orientation and whether you are reading the right marking.

A short practical routine

When you pick up an unknown ceramic capacitor, read the three digits, split them into figures and multiplier, and work out the picofarad value before converting to nanofarads or microfarads. Write the value on a label or in a parts list immediately, while the part is still in your hand, rather than trusting memory after sorting a dozen parts. For replacements, note voltage rating and type from the original part or the circuit documentation before ordering, and verify the new part's markings on arrival.

For related electronics maths, the Resistor Color Code Calculator decodes the equivalent system for resistors, and the Electricity Cost Calculator covers the power side of circuits. For more on working through numbers step by step, see How to Calculate an Average the Right Way.

The takeaway

A capacitor code is figures plus zeros, in picofarads: first two digits are the figures, the third digit counts the zeros, and dividing by 1,000 converts to nanofarads and microfarads. Memorise 104 as 0.1 microfarads, check units at every step, and remember that capacitance is only one part of a capacitor's specification.