How to calculate resistance of a resistor by using color code?

Lets say you have 10 resistors and no digital multimeter to check their values and you have been asked to find resistance of the each resistor provided. They all look the same so there is no easy way out to find out the values of their resistances. So as a solution to these problems the Radio Manufacturers Association assigned color codes for the resistors to easily identify the their resistance values.

How to find Resistor Values by Reading Color Code?

The question is what are these color codes and how do we obtain the value of resistor using these color codes. Before we go any further have a look at the diagram given below for a general idea of color codes in resistors:
color code

 As you can see the value of the resistor provided is 147 ohms with 0.5% permissible error. But how did we get this value? To understand this we need to first understand what is the meaning of the terms 'first' color band, multiplier band and tolerance band. So lets figure it out:
1. Significant Figures Color bands: The color bands except last two (multiplier and tolerance) correspond to the significant figures of the resistance value of resistor. The first color band is first significant digit, the second color band is second significant digit and the third one is the third digit. Note that the resistor above is 5 band resistor so has 3 significant figures and in all other cases you may expect 2 significant figures as in 4 band resistor.
2. Multiplier Band: This band indicates the number that we need to multiply with the significant figures to obtain the value of manufactured resistor. This is simply in terms of powers of 10 and can be studied from table below.
3. The tolerance band: This band has the only significance to indicate the errors permissible in the resistor. You can call it tolerance of resistor and might find its values as given below in table.


Now lets try out the example of the resistor we used above:

This resistor has brown color as first color band, so first significant figure is 1. 
It has yellow band as next band so the second significant figure is 4.
Final significant figure that means the third one is violet so its value is 7.

The multiplier is indicated by black color code and so its value is 1.
Finally we have the tolerance band with green color which represents 0.5% tolerance.

So that is how we obtain the value of resistor as 147 ohms with 0.5% tolerance.

So make a note to remember the table and values mentioned so that you may recognize the resistors easily. Many people have different Mnemonics to remember the color code order. Some use B B Roy of Great Britain has a Very Good Wife while others use Rainbow pattern called the ViBGYOR to identify the same.

That completes today's article and with this simple explanation I hope you have understood how to identify the values of resistors just by having a look at their color codes.

Got any questions? Please leave a comment below.


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