Compositions of color band(s) on a resistor is used to mark a resistor based on it’s ohm value.
For example a resistor with 5 band(s) :
The first band of a resistor is it’s first significant digit value, the second band determines it’s second significant digit value. The third band determines it’s third significant digit value. The fourth band determines it’s multiplier based on above tables. The last band determines it’s tolerance , if there’s no tolerance band means tolerance is 20%.
For example here we have a resistor with 4 band(s):
There’s a gap between gold and brown, we can determine the first band is brown.
Calculation is Simple:
The first band is brown = 1 , the second band is black = 0, third band is brown = 1, the gold band is gold means tolerance about 5%. Arrange first and second digit we got: 10, multiply it with 1 x 10 ohm = 10 x 10 = 100 ohm with tolerance about 5%.
To make it easy, we don’t have to remember the table, we can use an online resistor value calculator: