Capacitor code calculator

The first two digits are the value and the third says how many zeros follow. The answer is always in picofarads. So 104 is 10 followed by four zeros, 100 000 pF, which is 100 nF or 0.1 µF. 472 is 4700 pF, or 4.7 nF. The third digit is never a third figure of the value, and reading it as one is the usual first mistake.

Two third digits break the pattern. On small parts, 9 means multiply by 0.1 and 8 means multiply by 0.01, so 479 is 4.7 pF and 109 is 1 pF. The digit 7 is not used. A code ending in 0 has a trap of its own: 100 read as a code is 10 pF, but some older discs print small values in plain picofarads, so the same three characters can mean 100 pF. The calculator flags it when that happens.

A letter straight after the digits is the tolerance. J is ±5 %, K ±10 %, M ±20 %. Z is lopsided: the part may be 20 % low or 80 % high, which is common on cheap Y5V and Z5U ceramics. B, C and D are in picofarads rather than per cent, because a percentage of a 2 pF part is too small to be useful. The capacitor markings lesson covers the reading order and the polarity marks.

A digit followed by a letter, such as 2A or 1H, is the rated voltage. The digit is a power of ten and the letter gives the first figures: A is 1, so 2A is 1 × 10² = 100 V, and J is 6.3, so 2J is 630 V. Film capacitors print it on the box, and makers put it either side of the value, so 2A104K and 104K 2A mean the same part. J can be a tolerance or a voltage letter, and position settles which: a letter straight after the value digits is the tolerance, and a digit-and-letter pair standing apart from the value is the voltage. The capacitor ratings lesson explains how much margin to leave under that voltage.

The codes you meet most often, with the value in all three units. The calculator above reads any other code.

Tolerance letters as KEMET lists them for ceramic capacitors. Voltage codes checked against Nichicon film and electrolytic catalogues and the Panasonic electrolytic part-number guide. A code that follows the same rule but is missing here, such as 1D, still decodes, with a note to confirm it on the datasheet.

Most chip capacitors carry no marking at all. The ones that do use two characters: a letter for the first figures and a digit for the number of zeros, in picofarads, with 9 meaning ×0.1. S3 is 4.7 × 10³ pF, 4.7 nF. Some makers add their own letter in front, so KA2 is a KEMET part of 1.0 × 10² pF, 100 pF. Upper and lower case are different values, which is why the calculator keeps the case you type.

A code says what the part was sold as, not what it is now. Two parts marked 104K 50V can be a C0G ceramic that holds its value and an X7R that loses a large share of it under DC bias, and nothing on the body tells them apart; the ceramic capacitors lesson explains why. A bare number such as 22 can be picofarads on a ceramic or microfarads on an electrolytic. When the value matters, for a filter corner or a timing capacitor, measure it: the testing lesson shows how. Resistor markings have their own calculators: colour bands and SMD codes.

• Watch for a letter used as the decimal point. 4n7 is 4.7 nF and 2p2 is 2.2 pF, the same idea as the R in resistor codes.
• Discharge a capacitor before you measure it, and take it out of the circuit. A charged part can damage the meter, and parts in parallel make the reading wrong.
• On electrolytics the value is printed in µF, and the stripe marks the negative lead. Fitting one backwards can make it bulge or vent.
• Leave voltage margin on ceramics. An X7R part loses more of its value the closer the DC voltage gets to its rating, so a 50 V part on a 5 V rail keeps far more of its 100 nF than a 6.3 V one.
• For timing and filters, use C0G (also called NP0) ceramics or film capacitors. They hold their value with voltage and temperature, where X7R and Y5V do not.