Microcontroller Beginner Kit -
Finding the value of a resistor by reading it's color codes

To calculate the
value of a resistor using the color coded
stripes on the resistor, use the following
procedure.

Step
One: Turn the resistor so that the gold
or silver stripe is at the right end of the
resistor.

Step
Two: Look at the color of the first two
stripes on the left end. These correspond to the
first two digits of the resistor value. Use the
table given below to determine the first two
digits.

Step
Three: Look at the third stripe from the
left. This corresponds to a multiplication
value. Find the value using the table below.

Step
Four: Multiply the two digit number from
step two by the number from step three. This is
the value of the resistor n ohms. The fourth
stripe indicates the accuracy of the resistor. A
gold stripe means the value of the resistor may
vary by 5% from the value given by the stripes.

Resistor Color
Codes (with gold or silver strip on right end)

Color

First
Stripe

Second
Stripe

Third
Stripe

Fourth
Stripe

Black

0

0

x1

Brown

1

1

x10

Red

2

2

x100

Orange

3

3

x1,000

Yellow

4

4

x10,000

Green

5

5

x100,000

Blue

6

6

x1,000,000

Purple

7

7

Gray

8

8

White

9

9

Gold

5%

Silver

10%

Follow the
above procedure with the examples below and soon
you will be able to quickly determine the value
of a resistor by just a glance at the color
coded stripes.

Examples

Example1:

You are given a
resistor whose stripes are colored from left to
right as brown, black, orange, gold. Find the
resistance value.

Step
One: The gold stripe is on the right so
go to Step Two.

Step
Two: The first stripe is brown which has
a value of 1. The second stripe is black which
has a value of 0. Therefore the first two digits
of the resistance value are 10.

Step
Three: The third stripe is orange which
means x 1,000.

Step
Four: The value of the resistance is
found as 10 x 1000 = 10,000 ohms (10 kilohms =
10 kohms).

The gold stripe means
the actual value of the resistor mar vary by 5%
meaning the actual value will be somewhere
between 9,500 ohms and 10,500 ohms. (Since 5% of
10,000 = 0.05 x 10,000 = 500)

Example2:

You are given a
resistor whose stripes are colored from left to
right as orange, orange, brown, silver. Find the
resistance value.

Step
One: The silver stripe is on the right so
go to Step Two.

Step
Two: The first stripe is orange which has
a value of 3. The second stripe is orange which
has a value of 3. Therefore the first two digits
of the resistance value are 33.

Step
Three: The third stripe is brown which
means x 10.

Step
Four: The value of the resistance is
found as 33 x 10 = 330 ohms.

The silver stripe means
the actual value of the resistor mar vary by 10%
meaning the actual value will be between 297
ohms and 363 ohms. (Since 10% of 330 = 0.10 x
330 = 33)

Example3:

You are given
a resistor whose stripes are colored from left
to right as blue, gray, red, gold. Find the
resistance value.

Step
One: The gold stripe is on the right so
go to Step Two.

Step
Two: The first stripe is blue which has a
value of 6. The second stripe is gray which has
a value of 8. Therefore the first two digits of
the resistance value are 68.

Step
Three: The third stripe is red which
means x 100.

Step
Four: The value of the resistance is
found as 68 x 100 = 6800 ohms (6.8 kilohms = 6.8
kohms).

The gold stripe means
the actual value of the resistor mar vary by 5%
meaning the actual value will be somewhere
between 6,460 ohms and 7,140 ohms. (Since 5% of
6,800 = 0.05 x 6,800 = 340)

Example 4:

You are given a
resistor whose stripes are colored from left to
right as green, brown, black, gold. Find the
resistance value.

Step
One: The gold stripe is on the right so
go to Step Two.

Step
Two: The first stripe is green which has
a value of 5. The second stripe is brown which
has a value of 1. Therefore the first two digits
of the resistance value are 51.

Step
Three: The third stripe is black which
means x 1.

Step
Four: The value of the resistance is
found as 51 x 1 = 51 ohms.

The gold stripe means
the actual value of the resistor mar vary by 5%
meaning the actual value will be somewhere
between 48.45 ohms and 53.55 ohms. (Since 5% of
51 = 0.05 x 51 = 2.55)

Other
Resistor Information

There are some more
rules that may be useful when working with
resistors. You do not need to know them but if
you need a resistor with a value that you do not
have, you my be able to use the following
information to create the value of resistor you
need.

First Rule
for Resistors : Series Connection

When two resistors are
connected in series, as shown in Figure 1, the
new resistance between points A and B is R1 +
R2.

AB
Figure 1

The resistors add
together. For example if R1 = 500 ohms and R2 =
250 ohms then the resistance between points A
and B would be R1 + R2 = 500 + 250 = 750 ohms.

Second Rule
for Resistors : Parallel Connection

When two resistors are
connected in parallel, as shown in Figure 2, the
new resistance is smaller than either R1 or R2.
The new resistance between points A and B is (R1
x R2) / (R1 + R2).

A

B
Figure 2

For example, if R1 =
500 and R2 = 250 then the resistance between
points A and B = (500 x 250) / (500 + 250) =
(125,000) / (750) = 167 ohms. If R1 = R2 then
the new resistance is just R1 / 2.

Using these two rules,
resistors can be combined to form new resistance
values.