There are three commonly used compact value labeling codes for physically small capacitors: the colour ring or bar code, the three-digit numeric code and three character alphanumeric code.
| Col. | Num. | Alphanumeric | Value | |||||
|---|---|---|---|---|---|---|---|---|
| 108 | p10 | .10 | R10 | 0.10 pF | 0.00010 nF | 0.00000010 µF | 0.00000000010 mF | |
| 129 | 1p2 | 1.2 | 1R2 | 1.2 pF | 0.0012 nF | 0.0000012 µF | 0.0000000012 mF | |
| 150 | 15p | 15 | 15R | 15 pF | 0.015 nF | 0.000015 µF | 0.000000015 mF | |
| 181 | n18 | k18 | K18 | 180 pF | 0.18 nF | 0.00018 µF | 0.00000018 mF | |
| 222 | 2n2 | 2k2 | 2K2 | 2200 pF | 2.2 nF | 0.0022 µF | 0.0000022 mF | |
| 273 | 27n | 27k | 27K | 27000 pF | 27 nF | 0.027 µF | 0.000027 mF | |
| 334 | µ33 | u33 | M33 | 330000 pF | 330 nF | 0.33 µF | 0.00033 mF | |
| 395 | 3µ9 | 3u9 | 3M9 | 3900000 pF | 3900 nF | 3.9 µF | 0.0039 mF | |
| 47µ | 47u | 47M | 47000000 pF | 47000 nF | 47 µF | 0.047 mF | ||
| m56 | 560000000 pF | 560000 nF | 560 µF | 0.56 mF | ||||
| 6m8 | 6800000000 pF | 6800000 nF | 6800 µF | 6.8 mF | ||||
| 82m | 82000000000 pF | 82000000 nF | 82000 µF | 82 mF | ||||
The first two codes are equivalent in that each of the ten colours used represent a digit. The first two colours or digits represent the significant digits of the value, and the third the power of ten to multliply with (i. e. the number of trailing zeroes). The resulting number is the value in picofarads, pF.
However, only 0–5 (black to green) are used in the normal way for powers of ten. 6 (blue) and 7 (violet) are not used at all, and 8 (grey) and 9 (white) are used with the alternate values 8–10 = –2 and 9–10 = –1 (i. e. one hundredth and one tenth respectively).
Colour coded capacitors typically have more than three colour rings, and there is some variation as to which three rings denote the value. Usually it is the three leftmost or the three middle rings (the broadest ring, or the one closest to the end should be to the left). As capacitors typically have high tolerances, values from the E12 series is almost invariably used, so the correct reading will yield values beginning with 10, 12, 15, 18, 22, 27, 33, 39, 47, 56, 68 or 82.
A three-digit numeric code is often followed by an uppercase letter denoting tolerance. The most common are J, K or M denoting ±5 %, ±10 % and ±20 % respecively (the latter is also the default value in the absence of any letter). Z is also frequent, denoting a tolerance of –20/+80 %. The letter V is not used, so a number followed by V is the maximum voltage for the component.
On a capacitor marked both 273K and 100V, the latter simply means simply means that its operating voltage is up to 100 V, while the former signifies a value of 27 nF ±10 % (and has nothing to do with a temperature of –0.15 °C). On the other hand, 100 alone or 100M means 10 pF ±20 %.
The alphanumeric code consists of two digits plus a letter (in its proper form always an SI-prefix) before, between or after these. The value is found by replacing the letter with a decimal point, moving the letter to the end and adding the appropriate unit (in this case farads, F).
There are some commonly seen alternatives to the proper use of SI-prefixes on actual components. As picofarads is the default unit, the p may be replaced by a decimal point or the letter R (as on resistors in the 0.1–99 Ω range). Further, n may be replaced by k or even K, for kilo or 1000 picofarads! Similarly µ may be replaced by M (which can be seen either as mega or 1000000 picofarads, or as an alternate abbreviation of micro), or for technical reasons rendered as the Latin letter u.