Encyclopedia of Electrical Engineering

A wide variety of resistors, fixed or variable, are large enough to have
their resistance in ohms printed on the casing. Some, however, are too
small to have numbers printed on them, so a system of color coding is
used. For the thin-film resistor, four, five, or six bands may be used.
**Fig.No.1: **Color coding for fixed resistors.
**Fig.No.2: **Color coding
### Four-band scheme

For the four-band scheme, the bands are always read from the end
that has a band closest to it, as shown in (Fig.No.1). The bands are numbered
as shown in (Fig.no.2) for reference in the discussion to follow.
The number corresponding to each color is defined in (Fig.No.2)
The fourth band will be either 5% or 10% as defined by gold and
silver, respectively. To remember which color goes with which percent,
simply remember that 5% resistors cost more and gold is more
valuable than silver.
**Example 1:** Find the value of the resistor in Fig.No.1.

**Solution:** Reading from the band closest to the left edge, we find that
the first two colors of red and black represent the numbers 2 and 0,
respectively as shown in (Fig.no.2). The third band is brown, representing the number 1 for the power of the multiplier as follows:
$$ 20 \times 10^1Ω = 200Ω$$
Now for the fourth band of gold, representing a tolerance of 5%:
To find the range into which the manufacturer has guaranteed the resistor
will fall, first convert the 5% to a decimal number equals to 0.05. Then multiply the resistor value by this decimal number:
$$0.05(200) Ω = 10 Ω$$
Finally, add the resulting number to the resistor value to determine the
maximum value, and subtract the number to find the minimum value.
That is,
$$ \text{Maximum} = 200Ω + 10Ω = 210 Ω$$
$$ \text{Minimum} = 200Ω - 10Ω = 190Ω$$
Range = 190 Ω to 210 Ω
Using the above procedure, the smallest resistor that can be labeled
with the color code is 10 Ω.
This is demonstrated in the next example.
**Example 2:** Find the value of the resistor in Fig.No.3.

**Solution:** The first two colors are gray and red, representing the numbers
8 and 2, respectively. The third color is gold, representing a multiplier
of 0.1.
**Fig.no.3: **Example no.2
Using the multiplier, we obtain a resistance of
$$(0.1)(82 Ω) = 8.2 Ω$$
The fourth band is silver, representing a tolerance of 10%. Converting
to a decimal number and multiplying through yields 10% = 0.10 and
$$(0.1)(8.2Ω ) = 0.82Ω $$
$$\text{Maximum} = 8.2 Ω + 0.82 Ω = 9.02 Ω$$
$$\text{Minimum} = 8.2 Ω - 0.82 Ω = 7.38 Ω$$
so that Range = 7.38 Ω to 9.02 Ω
#### Five-band Color Code

Some manufacturers prefer to use a five-band color code. In such
cases, as shown in the top portion of Fig. No.4, three digits are provided
before the multiplier. The fifth band remains the tolerance indicator. If
the manufacturer decides to include the temperature coefficient, a sixth
band will appear as shown in the lower portion of Fig. No. 4, with the
color indicating the PPM level.
**Fig.no. 4: **Five-band color coding for fixed resistors.
For four, five, or six bands, if the tolerance is less than 5%, the following
colors are used to reflect the % tolerances: