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How to Calculate Resistance Using Color Code?

Electrical Engineering Featured image

Before using any resistor in the electrical circuit, you need to find out the resistance value of the resistor. Each resistor has a specific resistance value.

In a previous article about basics information about resistors, we have seen, there are four color bands on each resistor. And the resistance value of the resistor depends upon the color code/band printed on the resistor.

So the question is…

How to Calculate Resistance Using Color Code?

The color-coding of these color bands on the resistor is used to identify the value and tolerance. The power rating of the resistor depends upon the physical size of the resistor.

There are four different color bands (A, B, C and D printed on the resistor body) as shown in a below figure.

Resistor Color Coding

The first of three bands (A, B, C) which shows the different value. And the last band (D) shows the tolerance in percentage.

I explain calculating resistance value in detail. Please refer to the color band table given below.

 Table for Color Code Resistor

Here, each band position and its color has specific significance to calculate resistance value.

  1. Band A: In the color code of the first band (A) depicts the first digit of the numerical value of the resistance. (Says x)
  2. Band B: In the color code of the second band (B) represents the second digit of the numerical value of resistance. (Says y)
  3. Band C: In the color code of the third band (C) is the decimal multiplier and gives the number of zero after two digits. (Says z)
  4. Band D: In the color code of the fourth band (D) or last band shows the tolerance in percentage (%). (Says p)

So the final formula you can use to calculate resistance:

Resistance = ((10x + y) z) (p/100)

Note:

I know, it is not easy to remember the value corresponding to each color band. You can use this simple phrase to remember the sequence color band and its values.

BB ROY of Great Britain had a Very Good Wife.

Let’s take an Example:

Calculate Resistance of Resistor from Color Bands

Suppose, The resistor having four color bands A, B, C, and D are red, brown, orange and gold respectively as shown in the below diagram.

Firstly choose the value of color from the table.

Red Brown Orange Gold
2 1 1000 5%
  • First step

The Red band of the resistance value is 2 and the brown band of the resistance value is 1 from the table. The first two digits of the band show the value of resistance 2 and 1 i.e. 21.

  • Second Step

From the table, the third orange band has value 1000. Multiply this value to 21 i.e. 21×1000=21000 Ω.

  • Third Step

Last is the Gold band having tolerance value in 5% (0.05) from the table. 21000×0.05=1050.

Finally, we get the final value of resistance is 1050 Ω.

Once you know to calculate Resistance Using Color Code of resistors, it will be easy for you to design and using resistors in the electrical circuit.

If you have any queries, you can hit the comment in below comment box.

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Thanks for Reading!

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