Reading EIA Three-Digit Capacitor Codes
Small ceramic and film capacitors are too tiny to print a full value on, so manufacturers use a compact three-digit EIA code instead: the first two digits are significant figures, and the third digit is a power-of-ten multiplier — the same convention resistor color codes use, just in a different physical format.
A code of "104" means 10 x 10^4 picofarads = 100,000 pF = 100 nF = 0.1 µF — a value worth memorizing since it's one of the most common decoupling capacitor values in real circuits. The trailing tolerance letter (J, K, M, etc.) specifies how far the actual capacitance may legitimately vary from the nominal value, which matters for timing circuits and filters where precision affects the actual cutoff frequency or oscillation rate.
Misreading a capacitor code is a common source of "why doesn't my circuit work" debugging sessions, since a 10x or 100x value error looks like almost any other wiring mistake until you check the part markings against a reference.