Learn the different units of capacitance. Capacitors are measured in microfarads, nanofarads and picofarads. Each microfarad (μF) equals 1,000 nanofarads (nF). Each nanofarad equals 1,000 picofarads (pF).
Learn how to read the most clearly labeled surface-mounted capacitors. Often electrolytic capacitors have their capacitance value and voltage written out clearly. For example, a capacitor that reads 2.2 μF 50V has a capacitance of 2.2 microfarads and a maximum voltage of 50 volts.
Learn how the labeling of one and two-digit capacitors works. Some caps are labeled with only one or two numbers. These capacitors are measured in microfarads if they have a value of less than one and in picofarads if their value is 1 or greater. A capacitor that reads .02, for example, will have a capacitance of .02 μF (microfarads), or 20,000 pF (picofarads). A capacitor labeled 22, on the other hand, will have a value of 22 pF (picofarads).
Learn how to read the caps whthatich are labeled with one or two numbers and an "n", "p" or "μ." In these capacitors, the letter represents the unit, and its placement represents a decimal place. So a capacitor labeled 1n8 has a value of 1.8 nanofarads. A capacitor labeled p4 has a value of 0.4 picofarads.
Learn how to read the common three-number code. Capacitors are frequently labeled with three numbers, often accompanied by a letter (more on that later). The first two digits of the number represent the value of the cap, and the third is a multiplier. The entire thing is expressed in picofarads. So a capacitor that reads "241" has a value of 24 plus 1 zero, or 240 pF. A capacitor marked 475 would have a value of 4,700,000 pF, or 4.7 μF.
Learn to recognize the exceptions to the previous rule. The numbers 6 and 7 are not used at all as multipliers. "8" multiplies the value by 0.01, and "9" multiplies it by 0.1. So a capacitor with the number "339" would have a value of 3.3 picofarads, and one labeled "228" would have a value of .22 picofarads.
Learn the codes that show the accuracy of the capacitor, called tolerance codes. The letter "F" shows a tolerance of 1%, "G" of 2% and "J" of 5%. The links below show more tolerance codes and their meanings.