Page 65 - Triwatt Custom Lead Amp Builder's Guide

Appendix 3 - How to read 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 1 and 2 significant digits and the third is a multiplier code. Most of the time the last digit
st
nd
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.

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 0.1 µF capacitor.

Most kit builders don't need to go further but there is sometimes a tolerance code given by a single
letter.

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