Capacitor Code Table
| Letter | E24 value | ×0.1 pF | ×1 pF | ×10 pF | ×100 pF | ×1 nF | ×10 nF | ×100 nF |
|---|---|---|---|---|---|---|---|---|
| A | 1.0 | 0.10 pF | 1.0 pF | 10 pF | 100 pF | 1.0 nF | 10 nF | 100 nF |
| B | 1.1 | 0.11 pF | 1.1 pF | 11 pF | 110 pF | 1.1 nF | 11 nF | 110 nF |
| C | 1.2 | 0.12 pF | 1.2 pF | 12 pF | 120 pF | 1.2 nF | 12 nF | 120 nF |
| E | 1.5 | 0.15 pF | 1.5 pF | 15 pF | 150 pF | 1.5 nF | 15 nF | 150 nF |
| G | 1.8 | 0.18 pF | 1.8 pF | 18 pF | 180 pF | 1.8 nF | 18 nF | 180 nF |
| J | 2.2 | 0.22 pF | 2.2 pF | 22 pF | 220 pF | 2.2 nF | 22 nF | 220 nF |
| L | 2.7 | 0.27 pF | 2.7 pF | 27 pF | 270 pF | 2.7 nF | 27 nF | 270 nF |
| N | 3.3 | 0.33 pF | 3.3 pF | 33 pF | 330 pF | 3.3 nF | 33 nF | 330 nF |
| Q | 3.9 | 0.39 pF | 3.9 pF | 39 pF | 390 pF | 3.9 nF | 39 nF | 390 nF |
| S | 4.7 | 0.47 pF | 4.7 pF | 47 pF | 470 pF | 4.7 nF | 47 nF | 470 nF |
| U | 5.6 | 0.56 pF | 5.6 pF | 56 pF | 560 pF | 5.6 nF | 56 nF | 560 nF |
| W | 6.8 | 0.68 pF | 6.8 pF | 68 pF | 680 pF | 6.8 nF | 68 nF | 680 nF |
| Y | 8.2 | 0.82 pF | 8.2 pF | 82 pF | 820 pF | 8.2 nF | 82 nF | 820 nF |
A capacitor too small to print 0.000000047 F on (which is most capacitors) carries two characters instead: a letter for the significant figure and a digit for the multiplier. The letter runs the E24 series - A is 1.0, J is 2.2, S is 4.7, Z is 9.1 - twenty-four steps of roughly ten percent each; the digit is the power of ten in picofarads, with 0 meaning times 1 pF, 3 meaning times 1 nF, and the crucial exception 9 meaning times 0.1 pF, not times a billion pF. So A4 is 1.0 times 10 nanofarads = 10 nF, J4 is 2.2 times 10 nF = 22 nF, and S5 is 47 times 100 nanofarads... which the table reads off directly.
The system coexists with the three-digit code everyone meets first: 104 means 10 times ten-to-the-4th picofarads = 100 nF. Same base unit, same exponent idea, different notation - the three-digit form uses two significant digits (so 104 can be 10, 22, 47 followed by an exponent), while the letter form gives an exact E24 figure. You meet the letter codes on small MLCC surface-mount parts where three characters plus a tolerance would not fit, on precision film capacitors, and in catalogs. One more quiet feature: the 24 E24 values map onto 24 letters of the alphabet because I and O are skipped - too easy to read as 1 and 0 on a part this small.
How to use
- Decode left to right: first letter gives the significant figure from the E24 column, second character gives the multiplier column - the value sits at their intersection. J4: letter J = 2.2, digit 4 = times 10 nF, so 22 nF.
- Watch the two edge digits: 9 means multiply by 0.1 (C9 = 0.12 pF, a temperature-compensating mica value, not 120 million pF), and digits 6-8 continue past the table edge into microfarads (6 = 1 μF, 7 = 10 μF, 8 = 100 μF) - the full lattice runs 0.1 pF to 910 μF.
- Read a trailing letter as tolerance, not value: J = plus/minus 5%, K = plus/minus 10%, M = plus/minus 20%. Position disambiguates - the same letter J means 2.2 as the first character and 5% as the last one.
Frequently asked questions
Is J4 the same capacitor as 224?
No, and the comparison teaches both systems: J4 = 2.2 times ten-to-the-4th picofarads = 22,000 pF = 22 nF. The three-digit 224 = 22 times ten-to-the-4th = 220,000 pF = 220 nF - ten times larger. The letter-code J4 corresponds to 223 (22 times 10 to the 3rd = 22,000 pF): same value, different notation. The trap is that in the letter system the digit counts full decades of picofarads directly (4 means ten-to-the-4th pF), while in the three-digit system the third digit is the exponent applied to a two-digit prefix. Convert through picofarads every time: letter code to (E24 figure times 10^digit) pF, three-digit to (first-two-digits times 10^last-digit) pF, then compare.
Why does the digit 9 mean times 0.1 instead of a huge number?
Because the scale has to reach below 1 pF and there is no minus sign: a code digit of -1 is impossible to print, so 9 was drafted as the single-step-down exponent. C9 is 1.2 times 0.1 = 0.12 pF - the kind of value that appears in RF filter networks and temperature-compensating N750 ceramics, where single tenths of a picofarad matter. Anything ten-to-the-ninth picofarads (about 1 millifarad) does not exist as a practical capacitor technology - the largest aluminum electrolytics live in the farad range and are always direct-marked - so there was never a competing claim on the digit 9. If you ever decode a mysterious 0.12 pF part, it is not a typo: it is the code system working as designed at its smallest end.
Why are the letters I and O missing from the code table?
They were removed on purpose: on a component 1 mm long, a stamped O is one pixel away from a 0, and I from a 1 - so the EIA letter series runs A through Z skipping I and O, leaving 24 letters. That is exactly the count of the E24 preferred series (1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, 9.1 - twenty-four values of roughly 1.1x spacing), so the engineering alphabet maps one letter to one preferred value with nothing left over: A to H, J to N, P to Z. The same instinct shows up in resistor color codes and battery size letters - codes avoid ambiguous glyphs, because a misread marking is a wrong circuit.
Are lowercase letters on a capacitor a different system?
Yes - EIA also defines a lowercase series for significant figures that fall between the E24 steps: a is 2.5, d is 4.0, f is 5.0, m is 6.0, n is 7.0, t is 8.0, and similar. These appear on military-spec and custom-tolerance parts where the required value (say 2.5 pF or 6.0 pF) has no uppercase letter, since the uppercase series jumps from 2.4 (K) straight to 2.7 (L). The lowercase codes are the one place capacitor marking is case-sensitive - a K4 and a k4 are different values on a part that uses both - though in practice a given manufacturer uses one series or the other. If a lowercase letter appears on a consumer ceramic, it is more likely a dielectric or temperature-coefficient hint than a value code, which is another reason to confirm against the datasheet when the value matters.