E12 Resistor Series

The electronic color code is used to indicate the values or ratings of electronic components, usually for
resistors, but also for capacitors, inductors, and others. A separate code, the 25-pair color code, is used
to identify wires in some telecommunications cables.
The electronic color code was developed in the early 1920s by the Radio Manufacturers Association
(now part of Electronic Industries Alliance(EIA)), and was published as EIA-RS-279. The current
international standard is IEC 60062.published by International Electrotechnical Commission.
Colorbands were used because they were easily and cheaply printed on tiny components. However,
there were drawbacks, especially for color blind people. Overheating of a component or dirt
accumulation, may make it impossible to distinguish brown from red or orange. Advances in printing
technology have now made printed numbers practical on small components. Where passive
components come in surface mount packages, their values are identified with printed alphanumeric
codes instead of a color code.
The resistance value, tolerance, and wattage rating are generally printed onto the body of the resistor
as numbers or letters when the resistors body is big enough to read the print, such as large power
resistors. But when the resistor is small such as a 1/4W carbon or film type, these specifications must
be shown in some other manner as the print would be too small to read.
So to overcome this, small resistors use coloured painted bands to indicate both their resistive value
and their tolerance with the physical size of the resistor indicating its wattage rating. These coloured
painted bands produce a system of identification generally known as a Resistors Colour Code.
An international and universally accepted Resistor Colour Code Scheme was developed many years
ago as a simple and quick way of identifying a resistors ohmic value no matter what its size or condition.
It consists of a set of individual coloured rings or bands in spectral order representing each digit of the
resistors value.
The resistor colour code markings are always read one band at a time starting from the left to the right,
with the larger width tolerance band oriented to the right side indicating its tolerance. By matching the
colour of the first band with its associated number in the digit column of the colour chart below the first
digit is identified and this represents the first digit of the resistance value.

1. Electronic color code

The electronic color code is used to indicate the values or ratings of electronic components, usually for
resistors, but also for capacitors, inductors, and others. A separate code, the 25-pair color code, is used
to identify wires in some telecommunications cables.

The electronic color code was developed in the early 1920s by the Radio Manufacturers Association
(now part of Electronic Industries Alliance(EIA)), and was published as EIA-RS-279. The current
international standard is IEC 60062.published by International Electrotechnical Commission.

Colorbands were used because they were easily and cheaply printed on tiny components. However,
there were drawbacks, especially for color blind people. Overheating of a component or dirt
accumulation, may make it impossible to distinguish brown from red or orange. Advances in printing
technology have now made printed numbers practical on small components. Where passive
components come in surface mount packages, their values are identified with printed alphanumeric
codes instead of a color code.
The resistance value, tolerance, and wattage rating are generally printed onto the body of the resistor
as numbers or letters when the resistors body is big enough to read the print, such as large power
resistors. But when the resistor is small such as a 1/4W carbon or film type, these specifications must
be shown in some other manner as the print would be too small to read.
So to overcome this, small resistors use coloured painted bands to indicate both their resistive value
and their tolerance with the physical size of the resistor indicating its wattage rating. These coloured
painted bands produce a system of identification generally known as a Resistors Colour Code.
An international and universally accepted Resistor Colour Code Scheme was developed many years
ago as a simple and quick way of identifying a resistors ohmic value no matter what its size or condition.
It consists of a set of individual coloured rings or bands in spectral order representing each digit of the
resistors value.
The resistor colour code markings are always read one band at a time starting from the left to the right,
with the larger width tolerance band oriented to the right side indicating its tolerance. By matching the
colour of the first band with its associated number in the digit column of the colour chart below the first
digit is identified and this represents the first digit of the resistance value.
Again, by matching the colour of the second band with its associated number in the digit column of the
colour chart we get the second digit of the resistance value and so on. Then the resistor colour code is
read from left to right as illustrated below:

3. Co
lour Digit Multiplier Tolerance
Black 0 1
Brown 1 10 ± 1%
Red 2 100 ± 2%
Orange 3 1,000
Yellow 4 10,000
Green 5 100,000 ± 0.5%
Blue 6 1,000,000 ± 0.25%
Violet 7 10,000,000 ± 0.1%
Grey 8 ± 0.05%
White 9
Gold 0.1 ± 5%
Silver 0.01 ± 10%
None ± 20%

Calculating Resistor Values
The Resistor Colour Code system is all well and good but we need to understand how to apply it in
order to get the correct value of the resistor. The “left-hand” or the most significant coloured band is the
band which is nearest to a connecting lead with the colour coded bands being read from left-to-right as
follows;
Digit, Digit, Multiplier = Colour, Colour x 10
colour
in Ohm’s (Ω’s)
For example, a resistor has the following colored markings;
Yellow Violet Red = 4 7 2 = 4 7 x 10
2
= 4700Ω or 4k7.
The fourth and fifth bands are used to determine the percentage tolerance of the resistor. Resistor
tolerance is a measure of the resistors variation from the specified resistive value and is a consequence
of the manufacturing process and is expressed as a percentage of its “nominal” or preferred value.
Typical resistor tolerances for film resistors range from 1% to 10% while carbon resistors have
tolerances up to 20%. Resistors with tolerances lower than 2% are called precision resistors with the or
lower tolerance resistors being more expensive.
Most five band resistors are precision resistors with tolerances of either 1% or 2% while most of the
four band resistors have tolerances of 5%, 10% and 20%. The colour code used to denote the tolerance
rating of a resistor is given as;
Brown = 1%, Red = 2%, Gold = 5%, Silver = 10 %

4. If resistor has no fourth tolerance band then the default tolerance would be at 20%.
It is sometimes easier to remember the resistor colour code by using mnemonics or phrases that have
a separate word in the phrase to represent each of the Ten + Two colours in the code. However, these
sayings are often very crude but never the less effective for remembering the resistor colours. Here are
just a few of the more “cleaner” versions but many more exist:
 Bad Booze Rots Our Young Guts But Vodka Goes Well
 Bad Boys Ring Our Young Girls But Vicky Goes Without
 Bad Boys Ring Our Young Girls But Vicky Gives Willingly — Get Some Now (This one is only
slightly better because it includes the tolerance bands of Gold, Silver, and None).

A 100 kΩ, 5% axial-lead resistor A 2260 ohm, 1% precision resistor with 5 color bands,
from top 2-2-6-1-1; the last two brown bands indicate
the multiplier (x10), and the 1% tolerance. The larger
gap before the tolerance band is somewhat difficult to
distinguish.

5. From top to bottom:
 Green-Blue-Black-Black-Brown
o 56 ohms ± 1%
 Red-Red-Orange-Gold
o 22,000 ohms ± 5%
 Yellow-Violet-Brown-Gold
o 470 ohms ± 5%
 Blue-Gray-Black-Gold
o 68 ohms ± 5%
The physical size of a resistor is indicative of the power it can dissipate, not of its resistance.

References:
http://www.electronics-tutorials.ws/resistor/res_2.html
https://en.wikipedia.org/wiki/Electronic_color_code

6. Standard resistor values
In 1952 the IEC (International Electrotechnical Commission) decided to define the resistance and
tolerance values into a norm, to ease the mass manufacturing of resistors. These are referred to as
preferred values or E-series, and they are published in standard IEC 60063:1963. These standard
values are also valid for other components like capacitors, inductors and Zener diodes. The preferred
values for resistors were established in 1952, but the concept of the geometric series was already
introduced by army engineer Renard in the 1870s.
The standardization of resistor values serves several important purposes. When manufacturers
produce resistors with different resistance values, these end up approximately equally spaced on a
logarithmic scale. This helps the supplier to limit the number of different values that have to be produced
or kept in stock. By using standard values, resistors of different manufacturers are compatible for the
same design, which is favorable for the electrical engineer.
Aside from the preferred values, many other standards related to resistors exist. An example is standard
sizes for resistors, or the marking of resistors with color codes or numerical codes. Power ratings of
resistors are not defined in a norm, therefore often is deviated from the above described series.
Preferred values or E-series
 The EIA "E" series specify the preferred values for various tolerances. The number following
the "E" specifies the number of logarithmic steps per decade. The table below is normalized for
the decade between 100 and 1,000. The values in any decade can be derived by merely
dividing or multiplying the table entries by powers of 10. The series are as follows:
As basis the E12 has been developed. E12 means that every decade (0.1-1, 1-10, 10-100 etc) is divided
in 12 steps. The size of every step is equal to:
One could also say every value is 21% or 1.21 times higher than the last, rounded to whole numbers.
Because of this, all resistors with a tolerance of 10% overlap. The series looks as follows: 1– 1.2 – 1.5
– 1.8 – 2.2 – 2.7 – 3.3 – 3.9 – 4.7 – 5.6 – 6.8 – 8.2 – 10 etc. All these values can be powers of ten (1.2–
12 – 120 etc).

 E6 20%
 E12 10%
 E24 5% (also available with 1%)
 E48 2%
 E96 1%
 E192 0.5% (also used for resistors with 0.25% and 0.1%).

7. E6 Series at 20% Tolerance – Resistors values in Ω’s
1.0, 1.5, 2.2, 3.3, 4.7, 6.8
E12 Series at 10% Tolerance – Resistors values in Ω’s
1.0, 1.2, 1.5, 1.8, 2.2, 2.7, 3.3, 3.9, 4.7, 5.6, 6.8, 8.2
E24 Series at 5% Tolerance – Resistors values in Ω’s
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, 7.2, 8.2, 9.1
E96 Series at 1% Tolerance – Resistors values in Ω’s
1.00, 1.02, 1.05, 1.07, 1.10, 1.13, 1.15, 1.18, 1.21, 1.24, 1.27, 1.30, 1.33, 1.37, 1.40, 1.43,
1.47, 1.50, 1.54, 1.58, 1.62, 1.65, 1.69, 1.74, 1.78, 1.82, 1.87, 1.91, 1.96, 2.00, 2.05, 2.10,
2.15, 2.21, 2.26, 2.32, 2.37, 2.43, 2.49, 2.55, 2.61, 2.77, 2.74, 2.80, 2.87, 2.94, 3.01, 3.09,
3.16, 3.24, 3.32, 3.40, 3.48, 3.57, 3.65, 3.74, 3.83, 3.92, 4.02, 4.12, 4.22, 4.32, 4.42, 4.53,
4.64, 4.75, 4.87, 4.99, 5.11, 5.23, 5.36, 5.49, 5.62, 5.76, 5.90, 6.04, 6.19, 6.34, 6.49, 6.65,
6.81, 6.98, 7.15, 7.32, 7.50, 7.68, 7.87, 8.06, 8.25, 8.45, 8.66, 8.87, 9.09, 9.31, 9.53, 9.76

W
hile the "E" preferred value lists are the best way to insure one is stocking the optimum number of
values for a given tolerance, a word of caution is in order with respect to what is actually available in
the marketplace and certain real world practices. For instance, the E48 list is often used as a stock list
for 1% resistors for inventory control (48 values per decade rather than 96), but this practice leaves
"holes" or gaps in one's stock not covered by tolerance overlap, an undesirable practice in a prototype
lab (less of an issue to the digital designer than to an analog circuit designer). The use of the E48 list
for inventory control of 1% resistors works out well because every value on the E48 list just happens to
also appear on the E96 list; the holes are thus symmetrical and easily filled by acquisition of one of the
other 48 values per decade being omitted from stock. However, this is not always the case as can be
seen by comparing the E24 and E96 lists. Nevertheless, many manufacturers make every single value
on the E24 list in 1% tolerance even though the practice makes little mathematical sense (think about
the obvious tolerance overlap between the 120 and 121 values for instance). Stocking only the E24
series in 1% will result in less symmetrical holes in stock than the practice of stocking only the E48
series. In any event, one should be aware of these practices to avoid confusion.

8. E12 series (tolerance 10%)
10 12 15 18 22 27
33 39 47 56 68 82

T
he E12 series is probably the most common series and exist for almost every resistor. The tolerance
is ±10%.

The E12 series of resistor values, including their color codes.
References: http://www.resistorguide.com/resistor-values/

9. Q) Whenever I see a capacitor/resistor assortment that features the most "common" ones (which, I
understand can be quite subjective), they tend to come rated in powers of 1, 2.2 and 4.7. What's magical
about those numbers?
Is that some mathematical relationship in Ohm's law of which I'm not aware? Is it some logarithmic
progression for some OTHER electrical engineering formula that I've not yet encountered? As someone
who a scary uncanny knack for solving "find the pattern in this series of numbers" puzzles, it's killing
me that I can't figure this one out. :)
For the E12 series the step size is the 12th root of 10, or about 1.2 larger than the previous one, so 12
steps take you from 10 to 100. That goes with a 10 % tolerance: you can always find an E12 value
within 10 % of the desired value. That's because
√

9 5n21nnt5heE5n2n
1
C n21n

For
example: 18 Ω + 10 % = 19.8 Ω. The next E12 value is 22 Ω. Then 22 Ω - 10 % = 19.8 Ω. (It doesn't
always fit that neatly. The blue line shows a small gap between 12 Ω and 15 Ω, but most often there's an overlap.) Nowadays 10 % isn't used much anymore for resistors, 5 % is much more common, and 1 % is not that much more expensive.
That means your desired value won't fall into the 1 % tolerance of the E12 series. For example, if you
want a 20 Ω resistor the closest E12 values are 18 Ω and 22 Ω. With a 1 % tolerance hey don't come
closer than 18.18 Ω and 21.78 Ω, resp. That's why 1 % resistors are offered in a much larger range,
typically the E96 range, which includes 20 Ω.
When an engineer designs a circuit, they work out the component values which make it work as well as
possible. This may lead to values like 149 Ohms or 255,334 Ohms. The manufacturer then usually
chooses the closest value from the E12 series. Instead of 149 and 255,334 Ohms they would use 150
and 270k. Since each E12 value is about 20% bigger than the last, the nearest E12 is never in error by
more than about 10%. In practice this kind of error in resistor values rarely affects the behaviour of a
circuit. The large quantity of E12s used means that their price is low, keeping manufacturers happy!

10. Q) We often see component values of 4.7K Ohm, 470uF, or 0.47uH. For example, digikey has millions
of 4.7uF ceramic capacitors, and not a single 4.8uF or 4.6uF and only 1 listed for 4.5uF (specialty
product).
What's so special about the value 4.7 that sets so far apart from say 4.6 or 4.8 or even 4.4 since in the
3.. series we usually 3.3,33, etc. How did these numbers come to be so entrenched? Perhaps a
historical reason?
Have you ever noticed the dials on a scope are always 1-2-5-10-20-50-...? This has a simple and similar
reason, although the values on the dials are a bit more rounded for convenience.
Many phenomena are perceived as being logarithmic (the best known one being sound).
Look at this sequence:
n 10
22 47 100 220 470 1000
log(n) 1 1.34 1.67 2 2.34 2.67 3
See how nicely and evenly spaced they fit on every 1/3 and 2/3? You can't even see the line is slightly
curved.

11. The resistors/capacitors/inductors are pretty much similar. If you want an evenly divided range of
resistors you can simply pick the 10-22-47 values.
See how handy these values are? They are easy to do calculations, evenly spaced and therefore
commonly used. Remember that in 'the old days' computers and calculators weren't too common, so
values were chosen to make things as easy as possible.
These are the 13 resistors that span 10 to 100 in the old 10% series and they are 10, 12, 15, 18, 22,
27, 33, 39, 47, 56, 68, 82, 100. I've plotted the resistor number (1 to 13) against the log of resistance.
This, plus the desire for two-significant digits, looks like a good reason. I tried offsetting a few preferred
values by +/-1 and the graph wasn't as straight.
There are 12 values from 10 to 82 hence E12 series. There are 24 values in the E24 range.
Also the magic number for the E12 series is the 12th root of ten. This equals approximately 1.21152766
and is the theoretical ratio the next highest resistor value has to be compared to the current value i.e.
10K becomes 12.115k etc.
For the E24 series, the magic number is the 24th root of ten (not suprisingly)
It's interesting to note that a slightly better straight line is got with several values in the range reduced.
Here are the theoretical values to three significant digits: -
10.1, 12.1, 14.7, 17.8, 21.5, 26.1, 31.6, 38.3, 46.4, 56.2, 68.1 and 82.5
Clearly 27 ought to be 26, 33 ought to be 32, 39 ought to be 38 and 47 ought to be 46. Maybe 82 should
be 83 as well. Here's the graph of traditional E12 series (blue) versus exact (green):