May 2017 19
details, I can’t say for sure.
QI am trying to build a circuit from a scan of an old schematic and I noticed that the markings for the resistors show a value separated by a letter, e.g., “3K3” and “4K7.” Also, the
capacitors are shown as a value followed by a single
character such as “10n” and “100u.” I was wondering if
you knew the proper way to interpret/translate/convert
these markings as they are not at all what I am used to
ALet’s start with the resistors. They are pretty easy to decipher, but there are, in fact, several different marking methods in use. In the case of something like “3K3,” the letter K represents
a 1,000 multiplier and it also stands in the place of the
decimal point. So, “3K3” means 3,300 ohms ( 3. 3 x 1,000),
and “4K7” means 4,700 ohms. The letter M is also in use
as a 1,000,000 multiplier and R as simply 1. So, “5M6” is
5,600,000 ohms and “1R2” is 1.2 ohms.
Sadly, though, this isn’t the only way to mark resistors.
There is, of course, the resistor color code that we’re all
familiar with. Those include a tolerance in the last band,
but not always. Wikipedia has a summary of the meanings
of the various colors for value, multiplier, and tolerance at
also includes color coding for capacitors, which are quite
similar but with some important differences.
Then, there is another system without letters used
with SMD resistors that uses a three or four digit code.
The three digit code is used for resistors that are “standard
tolerance.” The four digit code is for more precision. This
coding scheme uses the right-most digit as the power of
10 multiplier — it’s essentially an exponent. You can think
of it as 1 followed by that number of zeros, so 3 indicates
1,000. The digits to the left of that show the number to
multiply, like a mantissa (though it’s not normalized).
For example, 471 would mean 47 x 101 = 470 ohms,
and 333 would mean 33 x 103 = 33,000 ohms. If there
is an R, that means the exponent is zero (effectively no
multiplier and no multiplier digit) and the decimal point
would be where the R is. For example, 15R0 is 15 ohms
and 3R70 is 3.70 ohms.
A new system has emerged as well called EIA-96 (or
E96) for 1% SMD resistors. There are other resistor series,
but 96 is the most common. It uses three characters that
are encoded with a chart of values. You have to refer to the
EIA-96 chart to find the value. There are two code digits,
followed by a single multiplier letter. You can put “EIA-96”
into your favorite search engine to find the table, but I’ve
included one in Figures 2 and 3.
Here are a couple of examples: 56C is broken down
into code 56 which is 374, and then C, indicating a
multiplier of 100, so 374 x 100 = 37,400 ohms. Another
might be 12Y, where 12 is the value 130 multiplied by Y or
0.01, resulting in 1.3 ohms.
For capacitors, markings like “100n” or “100nF” mean
100 microfarads. Sometimes you’ll see a slash for the
voltage, like “100n/10V” meaning that the capacitor is
QUESTIONS and ANSWERS
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n FIGURE 2. EIA-96 table of values and codes. n FIGURE 3. EIA-96 table of multipliers.