Reading Capacitor Codes
Large capacitor have the value printed plainly on them, such as 10.uF (Ten Micro Farads) but
smaller disk types along with plastic film types often have just 2 or three numbers on them?
First, most will have three numbers, but sometimes there are just two numbers. These are
read as Pico-Farads. An example: 47 printed on a small disk can be assumed to be 47 Pico-
Farads (or 47 puff as some like to say)
Now, what about the three numbers? It is somewhat similar to the resistor code. The first two
are the 1st and 2nd significant digits and the third is a multiplier code. Most of the time the last
digit tells you how many zeros to write after the first two digits, but the standard (EIA standard
RS-198) has a couple of curves that you probably will never see. But just to be complete here
it is in a table.
What these numbers don't tell us is the ESR rating of a capacitor. Despite popular belief
capacitors will often still have the correct value of capacitance when they fail. To truly check a
capacitor's condition, you need a meter that measures the ESR.
milli, micro, nano, pico
1 mili Farad (or any other unit) is 1/1,000th or .001 times the unit. (10-3)
1 micro = 1/1,000,000 or 0.000 001 times the unit (10-6 )
1 nano = 1/1,000,000,000 or 0.000 000 001 times the unit (10-9 )
1 pico = 1/1,000,000,000,000 or 0.000 000 000 001 times the unit (10-12 )
Table 1 Digit multipliers
Third digit Multiplier (this times the first two digits
gives you the value in Pico-Farads)
0 1
1 10
2 100
3 1,000
4 10,000
5 100,000
6 not used
7 not used
8 .01
9 .1
Now for an example: A capacitor marked 104 is 10 with 4 more zeros or 100,000pF which is
otherwise referred to as a .1 uF capacitor.
Most kit builders don't need to go further, but I know you want to learn more. Anyway, Just to
confuse you some more there is sometimes a tolerance code given by a single letter. I don't
know why there were picked in the order they are, except that it kind of follows the middle row
of keys on a typewriter.
So a 103J is a 10,000 pF with +/-5% tolerance
Table 2 Letter tolerance code
Letter symbol Tolerance of capacitor
B +/- 0.10%
C +/- 0.25%
D +/- 0.5%
E +/- 0.5%
F +/- 1%
G +/- 2%
H +/- 3%
J +/- 5%
K +/- 10%
M +/- 20%
N +/- 0.05%
P +100% ,-0%
Z +80%, -20%
Now to be really complicate things there is sometimes a letter-number-letter (like Z5U) code
that gives information. Table 3 shows how to read these cryptic codes. A 224 Z5U would be a
220,000 pF (or .22 uF) cap with a low temperature rating of -10 deg C a high temperature
rating of +85 Deg C and a tolerance of +22%,-56%.
Table 3 Dielectric codes
First
symbol
(a
letter)
Low
temperature
requirement
Second
symbol
(a
number)
High
Temperature
requirement
Third
Symbol
(a
letter)
MAX.
Capaci
tance
chang
e over
temper
ature
Z +10 deg. C 2 +45 deg. C A +1.0%
Y -30 deg. C 4 +65 deg. C B +/- 1.5%
X -55 deg. C 5 +85 deg. C C +/- 2.2%
6 +105 deg. C D +/- 3.3%
7 +125 deg. C E +/- 4.7%
F +/- 7.5%
P +/- 10.0%
R +/- 15.0%
S +/- 22.0%
T +22%,
-33%
U +22%,
-56%
V +22%,
-82%
There are some Capacitor color codes - the last dot is the tolerance code where brown is +/-
1% red +/-2% as in the resistor color code with two exceptions black is +/- 20% and white is
+/- 10% going backward the three dots to the left of the tolerance dot form the value in pF
There will be two or three more color dots before the value but they mean