How the 3-digit capacitor code system works
Where the two-figure-plus-multiplier code comes from, how the 8 and 9 multipliers work, and how to map a code to pF, nF and uF.
Why small capacitors use a printed code
A ceramic disc or a surface-mount chip is far too small to fit a value like 0.1 microfarads on its body, so manufacturers borrowed a compact scheme from the EIA. Two significant figures and a single multiplier digit describe capacitance from a fraction of a picofarad up to roughly a microfarad. The convention is understood worldwide, which is why the same 104 marking appears on parts from every major maker. Reading it correctly saves you from pulling a datasheet for every component on a board.
Significant figures and the multiplier
The first two digits are the significant figures and the third is a power-of-ten multiplier that counts zeros added to reach a value in picofarads. A code of 223 is therefore 22 with three zeros, giving 22000 pF or 22 nF, while 475 is 47 with five zeros, giving 4700000 pF or 4.7 uF. Because the base unit is always the picofarad, you convert to nanofarads by dividing by one thousand and to microfarads by dividing by one million. That single rule covers the vast majority of ceramic and film parts you will meet.
The special 8 and 9 multipliers
Powers of ten only reach downward so far before you need fractions, so the code reserves two digits for that. A multiplier of 9 means multiply by 0.1 and a multiplier of 8 means multiply by 0.01, both of which shrink rather than grow the value. This is how a code such as 479 lands on 4.7 pF instead of an implausible 47 billion picofarads. Keeping these two exceptions in mind prevents the classic mistake of reading a tiny high-frequency capacitor as an enormous one.
Reading the tolerance letter
Many capacitors add one letter after the digits to state how far the real value may drift from the marked one. Wide-tolerance bulk parts often carry K for 10% or M for 20%, while precision timing and filter parts use J for 5% or F for 1%. The very tightest small-value parts use B, C or D, which are quoted in absolute picofarads rather than a percentage. Matching the letter to the job matters most in oscillators and filters, where a loose part shifts the frequency you designed for.