1 µF, uF, or mF = 1 microfarad = 10-6 farads. (Careful — in other contexts, mF is the official abbreviation for millifarads, or 10-3 farads. ) 1 nF = 1 nanofarad = 10-9 farads. 1 pF, mmF, or uuF = 1 picofarad = 1 micromicrofarad = 10-12 farads.

Ignore capital letters in the units. For example, “MF” is just a variation on “mf. " (It is definitely not a megafarad, even though this is the official SI abbreviation. ) Don’t get thrown by “fd. " This is just another abbreviation for farad. For example, “mmfd” is the same as “mmf. " Beware single-letter markings such as “475m,” usually found on smaller capacitors. [2] X Research source See below for instructions.

If there is no percentage listed, look for a single letter after the capacitance value or on its own line. This may be code for a tolerance value, described below.

1 kV = 1,000 volts. See below if you suspect your capacitor uses a code for voltage (a single letter or one digit and one letter). If there is no symbol at all, reserve the cap for low-voltage circuits only. If you are building an AC circuit, look for a capacitor rated specifically for VAC. Do not use a DC capacitor unless you have an in-depth knowledge of how to convert the voltage rating, and how to use that type of capacitor safely in AC applications.

Some capacitors use a colored bar or a ring-shaped depression to show polarity. Traditionally, this mark designates the - end on an aluminum electrolytic capacitor (which are usually shaped like tin cans). On tantalum electrolytic capacitors (which are very small), this mark designates the + end. [5] X Research source (Disregard the bar if it contradicts a + or - sign, or if it is on a non-electrolytic capacitor. )

If your code starts with exactly two digits followed by a letter (e. g. 44M), the first two digits are the full capacitance code. Skip down to finding units. If one of the first two characters is a letter, skip down to letter systems. If the first three characters are all numbers, continue to the next step.

If the third digit is 0 through 6, add that many zeroes to the end of the number. (For example, 453 → 45 x 103 → 45,000. ) If the third digit is 8, multiply by 0. 01. (e. g. 278 → 27 x 0. 01 → 0. 27) If the third digit is 9, multiply by 0. 1. (e. g. 309 → 30 x 0. 1 → 3. 0)

B = ± 0. 1 pF. C = ± 0. 25 pF. D = ± 0. 5 pF for capacitors rated below 10 pF, or ± 0. 5% for capacitors above 10 pF. F = ± 1 pF or ± 1% (same system as D above). G = ± 2 pF or ± 2% (see above). J = ± 5%. K = ± 10%. M = ± 20%. Z = +80% / -20% (If you see no tolerance listed, assume this as the worst case scenario. [12] X Research source )

The first symbol shows minimum temperature. Z = 10ºC, Y = -30ºC, X = -55ºC. The second symbol shows maximum temperature. 2 = 45ºC, 4 = 65ºC, 5 = 85ºC, 6 = 105ºC, 7 = 125ºC. The third symbol shows variation in capacitance across this temperature range. This ranges from the most precise, A = ±1. 0%, to the least precise, V = +22. 0%/-82%. R, one of the most common symbols, represents a variation of ±15%. [14] X Research source

If the capacitor has one long code beginning with “CM” or “DM,” look up the U. S. military capacitor chart. If there is no code but a series of colored bands or dots, look up the capacitor color code. [16] X Research source