Capacitor Code Calculator

Small ceramic and film capacitors are too small to print a number on, so they carry a compact code instead. The three-digit EIA form is two significant digits followed by a multiplier — the count of zeros, with the result in picofarads. 104 is 10 followed by four zeros: 100,000 pF, which is 100 nF, which is 0.1 µF, three names for one component. 223 is 22 nF and 475 is 4.7 µF. In the multiplier position, 8 and 9 are exceptions meaning ×0.01 and ×0.1, so 479 is 4.7 pF. An R acts as a decimal point for small values, making 4R7 another way to write 4.7 pF, and a trailing letter gives the tolerance: J is ±5%, K is ±10%, M is ±20%.

The first thing to check is whether you are even looking at a code. A part marked 47 is 47 picofarads read directly, not 47 followed by nothing — two-digit markings are literal values, and only three digits carry a multiplier. Electrolytics do not use this system at all; they have room to print the value and the voltage on the can, in microfarads.

What the code cannot tell you is the two things most likely to matter. The voltage rating is not in it — a 100 nF part rated 16 V and one rated 100 V carry identical markings — and neither is the dielectric class, which decides how much of that capacitance you actually get. A C0G or NP0 part holds its value to a few tens of parts per million across temperature. An X7R drifts up to ±15% over its range, and a Y5V is specified at +22% and −82%, meaning a nominal 100 nF may legitimately deliver 18 nF at the edge of its temperature band.

Class 2 ceramics also lose capacitance under DC bias, and this is not in any marking either. A large-value X5R or X7R in a small package can fall to half its rated value or less at the voltage it is actually working at, which is why a decoupling capacitor that measures correctly on a meter can still behave like something much smaller in the circuit. The code decodes a nominal value; the datasheet tells you what you will get.