Resistor Color Codes
Electric Technology

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About Resistance:


A conductor shows a property of resistance by virtue of which it opposes the flow of electric current through it. As it opposes the flow of electric current, it can be inferred from it that as the resistance increases, the flow of electric current decreases for a given potential difference.

By the above discussion, we can say that resistance is defined as the ratio of the potential difference applied across the conductor to the current flowing through it.

R= V/I

S.I. unit of resistance is the ohm. If the potential difference is 1 volt and current is 1 ampere then the resistance is 1 ohm.
Wire bound resistors and carbon resistors are basically two varieties of commercial resistors used.


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Any substance or material that has some resistance is called a resistor. The examples of the type of resistors are fixed resistor, variable resistor, and potential divider.

Constantan and Manganin are alloys used for making standard resistors because they have high resistivity, small temperature coefficient and are least affected by atmospheric conditions like moisture, air extra.

Factors affecting the resistance:

Area of cross-section: the resistance is inversely proportional to the area of cross-section.

Length: the resistance is directly proportional to the length of the wire.

Nature of the material: the resistance highly depends on the nature of the material used.

Resistivity or specific resistance:

The specific resistance is defined as the resistance of the conducting material having unit length and unit area of cross-section or, it is the resistance offered by the unit cube of the material of a conducting material.

S.I. unit of resistivity or specific resistance is ohm meter.


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The conductance is the ease with which current flows.

G= 1/resistance


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It is defined as reciprocal of resistivity.

Classification on the basis of resistivity:

On the basis of resistivity materials are classified into three types:





A material is said to be conductor if it has low resistivity and it ranges from 10-8 to 10-6 ohm meter. For example iron, copper.


A material is said to be insulator if it has high resistivity and it is more than 104-ohm meter. Plastics and Diamond are an example of insulators.


A material is said to be semiconductor if its resistivity lies between conductor and insulator. N-type semiconductor and P-type semiconductors are an example of semiconductors.

Now let us learn how we can measure resistance:

By practical approach:

Connect ammeter and battery in series with the wire and voltmeter in parallel. Measure the readings carefully and by applying ohms law discussed before you can calculate the resistance.

By using color codes:

If you will see any resistor, you will observe a few color lines on it, these colored lines can be used for identifying the value of ohm of the resistor and its percentage of accuracy.

   Colour     Letternumbermultipliercolourtolerance
RedR2102No fourth band20%

For remembering purpose:

B B ROY of Great Britain had Very Good Wife and by the table above figure out the corresponding number of the multiplier. For remembering tolerance there is no short trick.

Method to use color code:

The first band represents the first significant figure.

The second band represents the second significant figure.

The third band indicates the power of ten with two significant figures explained in points one and two.

The fourth band represents tolerance or we can call variation in percent.

For example: suppose lines are of red, red, red and silver the resistance value will be:

Red= 2, red=2, red=2 and for silver= plus-minus 10 percent.
The answer will be 22 x 102 ohm with plus-minus 10 percent tolerance.

Equivalent resistance in series and parallel:

In designing any circuit there exist various resistors arranged in different kinds of fashion. For the finding equivalent resistance, we classify resistance in series and parallel. In the electrical circuit, after evaluating equivalent resistance we can replace it by single resistance such that there is no change inflow of current.

Resistance in series:

When various resistors are connected in the end to end fashion such that current flows through them are the same. The total electric potential is adequate to the sum of an electric potential across individual resistances. The equivalent resistance is larger than that of individual resistance.

Rs= R1+R2+R3+………

Resistance in parallel:

When various resistors are connected in between two common points such that each of them is provided with a separate path for current flow. In parallel combination potential drop across each resistance is the same. The sum of the current through individual resistances is equal to the total current and the equivalent resistance is less than the smallest individual resistance.

RP= 1/R1+ 1/R2+1/R3+…….

(image source google search)

Dewakar Pandey
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