Resistor Color Codes Explained

Introduction:

In resistors, different colors are used as codes to specify the resistance value. This is because resistors are usually tiny, and it is challenging to print resistance values on them. Therefore, color bands are printed on them to represent their electrical resistance. These color bands are known as resistor color codes, which were invented in the 1920s by the Radio Manufacturers Association (RMA). This article explains how you can find the resistance value of a resistor from the color codes printed on them. 

What is Resistor Color Code?

The resistor color code is a standardized system used to identify the resistance value, tolerance, and temperature coefficient of a resistor. It can be identified as a series of color bands or stripes on the resistor's body, each representing a specific digit or parameter. The commercially available resistors have either 4, 5, or 6 bands with a specific resistance value. 

4 Band Resistor

4 band resistors are the resistors with 4 color bands. The first two bands on the resistor define the first two digits of the resistance value. The third band defines the multiplying factor for the resistor, while the fourth band defines the tolerance value of the resistance. The resistance value changes depending on the color of the resistor. 

 

Here's a table that defines the relationship between the different colors on the resistor band and the value represented by each color: 

 

 

In the above table, the first two columns define the first two color bands of the resistor. Similarly, the next two columns define the multiplying factor as well as the tolerance value for the resistor. For example, if the first two colors of a 4-band resistor are red and black, respectively, by using the table above, the red color band represents the value of 2 in the 1st digit column, while the black color band represents 0 in the 2nd digit column. 

 

Now, if the same 4-band resistor has a third and fourth color of green and silver, respectively, the green color represents the multiplying factor of 105 and the silver color represents a tolerance value of 10%. By combining all these four values, we will obtain a total resistor value of 20×105 ± 10%, or 2MΩ ± 10%. 

 

For better practice, you can imagine different 4-band resistors with different colors and determine the resistance value with the above table. Sometimes, in this 4-band resistor, you may discover that the fourth band is missing. In that case, it represents the tolerance value of 20%. 

5 Band Resistor

5 band resistors are the resistors with 5 color bands. The first three color bands define the first three digits of the resistance value, the fourth band defines the multiplying factor for the resistor; and the fifth band defines the tolerance value for the resistor. The same table used for the 4-band resistor can also be used for the 5-band resistor, but we need to include a column for the third digit. 

 

For example, let's imagine that we have a 5-band resistor and the first color band is red, the second color band is black, the third color band is green, the fourth color band is orange, and the fifth color band is silver. By referring to the table we initially used, the red band represents a value of 2 in the 1st digit column, the black band represents a value of 0 in the 2nd digit column, the green band represents a value of 5 in the 3rd digit column, the orange band defines the multiplying factor of 103 , and the silver band represents the tolerance value of 10%.

 

By combining all the different values, we will obtain a total resistance value of 205× 103 ±10% or 205KΩ ±10%. Usually, these 5-band resistors are used in calculations that require more accuracy. 

6-Band Resistor

6-band resistors are those with six color bands. The first three color bands represent the first three digits of the resistance value; the fourth band represents the multiplying factor for the resistor; the fifth band represents the tolerance value; and the sixth band defines the temperature coefficient of resistance. 

 

Here's a table that shows the relevant values for the 6-band resistor color coding.

 

 

By using the above table, let's imagine there is a 6-band resistor, and the first band is orange, the second band is yellow, the third band is green, the fourth band is brown, the fifth band is violence, and the sixth band is blue. What would be the resistance value? The orange band represents a value of 3 in the 1st digit column, the yellow band represents a value of 4 in the 2nd digit column, and the green band represents a value of 5 in the 3rd digit column. 

 

Similarly, the brown band defines a multiplying factor of 101, the violet band has a tolerance value of 0.1%, and the blue band represents a temperature coefficient of 10 ppm/k. Therefore, the total resistance value is 3.45KΩ ± 0.1% (10 ppm/k). 

SMD Resistor Coding

 

The SMD, or surface mount resistor, is a tiny rectangular resistor with silver conducting edges on two sides. It is used in the production of televisions, smartphones, and high-tech R&D equipment. If you closely observe the printed circuit boards of this electronic equipment, you will see a small code on top of the SMD resistors. The code is what defines the value of the resistor based on the type of coding scheme used. These coding schemes include 3 digits, 4 digits, and EIA 96 SMD resistor coding.

3 Digit Coding Scheme

In this scheme, three digits are used to define the value of the resistors, but the first two digits are the most significant digits, while the third digit defines the multiplying factor of the resistor. For example, a code of 223 on an SMD resistor means 22×103Ω or 22KΩ. Similarly, for a code of 430, the value of the resistor is either 43×100Ω or 43Ω. Furthermore, the letter R is usually used to define the position of the decimal point in the resistor. For example, if the code on the resistor is 2R2, it means the resistor value is 2.2Ω.

4 Digit Coding Scheme

In this scheme, the first three digits represent the three most significant digits of the resistor value, while the last digit defines the multiplying factor for the resistor value. For example, if the code on the surface mount resistor is 1001, the resistance value is either 100×101Ω or 1KΩ. Similarly, for a code of 5103, the resistor value is either 510×103Ω or 510KΩ. This 4-digit scheme is similar to the 3-digit scheme because the letter “R” is also used to define the position of the decimal point. Therefore, if the code on the resistor is 2R70, it means the resistor has a value of 2.70 Ω. 

EIA 96 SMD Coding Scheme

The EIA 96 coding scheme is used for the resistors, which have a tolerance of 1%. In this scheme, three characters are used to define the resistor value. The first two characters are usually two numbers, while the third character is usually a capital letter. The illustration below shows the SMD resistor code chart: 

 

 

By using the code chart above, let's derive the resistance value for an SMD code of 36C. The first two digits of this code are 36, and the corresponding value represented by the code is 232. In addition, the letter “C” has a multiplying factor of 100. Therefore, the value of the resistor is 232×100Ω, or 23.2Ω. 

Conclusion

The resistor color code is a simple yet powerful tool for quickly identifying the value, tolerance, and temperature coefficient of a resistor. In this guide, we have learned the calculation skills required to tackle the most complex electronic projects on resistor color codes. Take your electronics to the next level with our high quality resistors. We are excited to have you as our esteemed customer!